linux-toradex.git/kernel, branch v4.4.40 Linux kernel for Apalis and Colibri modules kernel/debug/debug_core.c: more properly delay for secondary CPUs 2017-01-06T10:16:16+00:00 Douglas Anderson dianders@chromium.org 2016-12-14T23:05:49+00:00 f93777c915446c772761b7d8f6eb7ef49eca4e63 commit 2d13bb6494c807bcf3f78af0e96c0b8615a94385 upstream. We've got a delay loop waiting for secondary CPUs. That loop uses loops_per_jiffy. However, loops_per_jiffy doesn't actually mean how many tight loops make up a jiffy on all architectures. It is quite common to see things like this in the boot log: Calibrating delay loop (skipped), value calculated using timer frequency.. 48.00 BogoMIPS (lpj=24000) In my case I was seeing lots of cases where other CPUs timed out entering the debugger only to print their stack crawls shortly after the kdb> prompt was written. Elsewhere in kgdb we already use udelay(), so that should be safe enough to use to implement our timeout. We'll delay 1 ms for 1000 times, which should give us a full second of delay (just like the old code wanted) but allow us to notice that we're done every 1 ms. [akpm@linux-foundation.org: simplifications, per Daniel] Link: http://lkml.kernel.org/r/1477091361-2039-1-git-send-email-dianders@chromium.org Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org> Cc: Jason Wessel <jason.wessel@windriver.com> Cc: Brian Norris <briannorris@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 2d13bb6494c807bcf3f78af0e96c0b8615a94385 upstream.

We've got a delay loop waiting for secondary CPUs.  That loop uses
loops_per_jiffy.  However, loops_per_jiffy doesn't actually mean how
many tight loops make up a jiffy on all architectures.  It is quite
common to see things like this in the boot log:

  Calibrating delay loop (skipped), value calculated using timer
  frequency.. 48.00 BogoMIPS (lpj=24000)

In my case I was seeing lots of cases where other CPUs timed out
entering the debugger only to print their stack crawls shortly after the
kdb> prompt was written.

Elsewhere in kgdb we already use udelay(), so that should be safe enough
to use to implement our timeout.  We'll delay 1 ms for 1000 times, which
should give us a full second of delay (just like the old code wanted)
but allow us to notice that we're done every 1 ms.

[akpm@linux-foundation.org: simplifications, per Daniel]
Link: http://lkml.kernel.org/r/1477091361-2039-1-git-send-email-dianders@chromium.org
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Brian Norris <briannorris@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
kernel/watchdog: use nmi registers snapshot in hardlockup handler 2017-01-06T10:16:16+00:00 Konstantin Khlebnikov khlebnikov@yandex-team.ru 2016-12-14T23:04:04+00:00 f2b8b3455b22405237110d929f107318a535a480 commit 4d1f0fb096aedea7bb5489af93498a82e467c480 upstream. NMI handler doesn't call set_irq_regs(), it's set only by normal IRQ. Thus get_irq_regs() returns NULL or stale registers snapshot with IP/SP pointing to the code interrupted by IRQ which was interrupted by NMI. NULL isn't a problem: in this case watchdog calls dump_stack() and prints full stack trace including NMI. But if we're stuck in IRQ handler then NMI watchlog will print stack trace without IRQ part at all. This patch uses registers snapshot passed into NMI handler as arguments: these registers point exactly to the instruction interrupted by NMI. Fixes: 55537871ef66 ("kernel/watchdog.c: perform all-CPU backtrace in case of hard lockup") Link: http://lkml.kernel.org/r/146771764784.86724.6006627197118544150.stgit@buzz Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Aaron Tomlin <atomlin@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 4d1f0fb096aedea7bb5489af93498a82e467c480 upstream.

NMI handler doesn't call set_irq_regs(), it's set only by normal IRQ.
Thus get_irq_regs() returns NULL or stale registers snapshot with IP/SP
pointing to the code interrupted by IRQ which was interrupted by NMI.
NULL isn't a problem: in this case watchdog calls dump_stack() and
prints full stack trace including NMI.  But if we're stuck in IRQ
handler then NMI watchlog will print stack trace without IRQ part at
all.

This patch uses registers snapshot passed into NMI handler as arguments:
these registers point exactly to the instruction interrupted by NMI.

Fixes: 55537871ef66 ("kernel/watchdog.c: perform all-CPU backtrace in case of hard lockup")
Link: http://lkml.kernel.org/r/146771764784.86724.6006627197118544150.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Aaron Tomlin <atomlin@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
exec: Ensure mm->user_ns contains the execed files 2017-01-06T10:16:14+00:00 Eric W. Biederman ebiederm@xmission.com 2016-11-17T04:06:51+00:00 b35f34f66943fa1b8feadb037d054a141723f7fe commit f84df2a6f268de584a201e8911384a2d244876e3 upstream. When the user namespace support was merged the need to prevent ptrace from revealing the contents of an unreadable executable was overlooked. Correct this oversight by ensuring that the executed file or files are in mm->user_ns, by adjusting mm->user_ns. Use the new function privileged_wrt_inode_uidgid to see if the executable is a member of the user namespace, and as such if having CAP_SYS_PTRACE in the user namespace should allow tracing the executable. If not update mm->user_ns to the parent user namespace until an appropriate parent is found. Reported-by: Jann Horn <jann@thejh.net> Fixes: 9e4a36ece652 ("userns: Fail exec for suid and sgid binaries with ids outside our user namespace.") Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit f84df2a6f268de584a201e8911384a2d244876e3 upstream.

When the user namespace support was merged the need to prevent
ptrace from revealing the contents of an unreadable executable
was overlooked.

Correct this oversight by ensuring that the executed file
or files are in mm->user_ns, by adjusting mm->user_ns.

Use the new function privileged_wrt_inode_uidgid to see if
the executable is a member of the user namespace, and as such
if having CAP_SYS_PTRACE in the user namespace should allow
tracing the executable.  If not update mm->user_ns to
the parent user namespace until an appropriate parent is found.

Reported-by: Jann Horn <jann@thejh.net>
Fixes: 9e4a36ece652 ("userns: Fail exec for suid and sgid binaries with ids outside our user namespace.")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
ptrace: Capture the ptracer's creds not PT_PTRACE_CAP 2017-01-06T10:16:11+00:00 Eric W. Biederman ebiederm@xmission.com 2016-11-15T00:48:07+00:00 1c1f15f8ebfbd5042883a1c9ae4b18a6299c9c5f commit 64b875f7ac8a5d60a4e191479299e931ee949b67 upstream. When the flag PT_PTRACE_CAP was added the PTRACE_TRACEME path was overlooked. This can result in incorrect behavior when an application like strace traces an exec of a setuid executable. Further PT_PTRACE_CAP does not have enough information for making good security decisions as it does not report which user namespace the capability is in. This has already allowed one mistake through insufficient granulariy. I found this issue when I was testing another corner case of exec and discovered that I could not get strace to set PT_PTRACE_CAP even when running strace as root with a full set of caps. This change fixes the above issue with strace allowing stracing as root a setuid executable without disabling setuid. More fundamentaly this change allows what is allowable at all times, by using the correct information in it's decision. Fixes: 4214e42f96d4 ("v2.4.9.11 -> v2.4.9.12") Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 64b875f7ac8a5d60a4e191479299e931ee949b67 upstream.

When the flag PT_PTRACE_CAP was added the PTRACE_TRACEME path was
overlooked.  This can result in incorrect behavior when an application
like strace traces an exec of a setuid executable.

Further PT_PTRACE_CAP does not have enough information for making good
security decisions as it does not report which user namespace the
capability is in.  This has already allowed one mistake through
insufficient granulariy.

I found this issue when I was testing another corner case of exec and
discovered that I could not get strace to set PT_PTRACE_CAP even when
running strace as root with a full set of caps.

This change fixes the above issue with strace allowing stracing as
root a setuid executable without disabling setuid.  More fundamentaly
this change allows what is allowable at all times, by using the correct
information in it's decision.

Fixes: 4214e42f96d4 ("v2.4.9.11 -> v2.4.9.12")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
mm: Add a user_ns owner to mm_struct and fix ptrace permission checks 2017-01-06T10:16:11+00:00 Eric W. Biederman ebiederm@xmission.com 2016-10-14T02:23:16+00:00 03eed7afbc09e061f66b448daf7863174c3dc3f3 commit bfedb589252c01fa505ac9f6f2a3d5d68d707ef4 upstream. During exec dumpable is cleared if the file that is being executed is not readable by the user executing the file. A bug in ptrace_may_access allows reading the file if the executable happens to enter into a subordinate user namespace (aka clone(CLONE_NEWUSER), unshare(CLONE_NEWUSER), or setns(fd, CLONE_NEWUSER). This problem is fixed with only necessary userspace breakage by adding a user namespace owner to mm_struct, captured at the time of exec, so it is clear in which user namespace CAP_SYS_PTRACE must be present in to be able to safely give read permission to the executable. The function ptrace_may_access is modified to verify that the ptracer has CAP_SYS_ADMIN in task->mm->user_ns instead of task->cred->user_ns. This ensures that if the task changes it's cred into a subordinate user namespace it does not become ptraceable. The function ptrace_attach is modified to only set PT_PTRACE_CAP when CAP_SYS_PTRACE is held over task->mm->user_ns. The intent of PT_PTRACE_CAP is to be a flag to note that whatever permission changes the task might go through the tracer has sufficient permissions for it not to be an issue. task->cred->user_ns is always the same as or descendent of mm->user_ns. Which guarantees that having CAP_SYS_PTRACE over mm->user_ns is the worst case for the tasks credentials. To prevent regressions mm->dumpable and mm->user_ns are not considered when a task has no mm. As simply failing ptrace_may_attach causes regressions in privileged applications attempting to read things such as /proc/<pid>/stat Acked-by: Kees Cook <keescook@chromium.org> Tested-by: Cyrill Gorcunov <gorcunov@openvz.org> Fixes: 8409cca70561 ("userns: allow ptrace from non-init user namespaces") Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit bfedb589252c01fa505ac9f6f2a3d5d68d707ef4 upstream.

During exec dumpable is cleared if the file that is being executed is
not readable by the user executing the file.  A bug in
ptrace_may_access allows reading the file if the executable happens to
enter into a subordinate user namespace (aka clone(CLONE_NEWUSER),
unshare(CLONE_NEWUSER), or setns(fd, CLONE_NEWUSER).

This problem is fixed with only necessary userspace breakage by adding
a user namespace owner to mm_struct, captured at the time of exec, so
it is clear in which user namespace CAP_SYS_PTRACE must be present in
to be able to safely give read permission to the executable.

The function ptrace_may_access is modified to verify that the ptracer
has CAP_SYS_ADMIN in task->mm->user_ns instead of task->cred->user_ns.
This ensures that if the task changes it's cred into a subordinate
user namespace it does not become ptraceable.

The function ptrace_attach is modified to only set PT_PTRACE_CAP when
CAP_SYS_PTRACE is held over task->mm->user_ns.  The intent of
PT_PTRACE_CAP is to be a flag to note that whatever permission changes
the task might go through the tracer has sufficient permissions for
it not to be an issue.  task->cred->user_ns is always the same
as or descendent of mm->user_ns.  Which guarantees that having
CAP_SYS_PTRACE over mm->user_ns is the worst case for the tasks
credentials.

To prevent regressions mm->dumpable and mm->user_ns are not considered
when a task has no mm.  As simply failing ptrace_may_attach causes
regressions in privileged applications attempting to read things
such as /proc/<pid>/stat

Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Cyrill Gorcunov <gorcunov@openvz.org>
Fixes: 8409cca70561 ("userns: allow ptrace from non-init user namespaces")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
hotplug: Make register and unregister notifier API symmetric 2016-12-15T16:49:23+00:00 Michal Hocko mhocko@suse.com 2016-12-07T13:54:38+00:00 1c0f4e0ebb791cad8fee77d8de1ceb684e631698 commit 777c6e0daebb3fcefbbd6f620410a946b07ef6d0 upstream. Yu Zhao has noticed that __unregister_cpu_notifier only unregisters its notifiers when HOTPLUG_CPU=y while the registration might succeed even when HOTPLUG_CPU=n if MODULE is enabled. This means that e.g. zswap might keep a stale notifier on the list on the manual clean up during the pool tear down and thus corrupt the list. Resulting in the following [ 144.964346] BUG: unable to handle kernel paging request at ffff880658a2be78 [ 144.971337] IP: [<ffffffffa290b00b>] raw_notifier_chain_register+0x1b/0x40 <snipped> [ 145.122628] Call Trace: [ 145.125086] [<ffffffffa28e5cf8>] __register_cpu_notifier+0x18/0x20 [ 145.131350] [<ffffffffa2a5dd73>] zswap_pool_create+0x273/0x400 [ 145.137268] [<ffffffffa2a5e0fc>] __zswap_param_set+0x1fc/0x300 [ 145.143188] [<ffffffffa2944c1d>] ? trace_hardirqs_on+0xd/0x10 [ 145.149018] [<ffffffffa2908798>] ? kernel_param_lock+0x28/0x30 [ 145.154940] [<ffffffffa2a3e8cf>] ? __might_fault+0x4f/0xa0 [ 145.160511] [<ffffffffa2a5e237>] zswap_compressor_param_set+0x17/0x20 [ 145.167035] [<ffffffffa2908d3c>] param_attr_store+0x5c/0xb0 [ 145.172694] [<ffffffffa290848d>] module_attr_store+0x1d/0x30 [ 145.178443] [<ffffffffa2b2b41f>] sysfs_kf_write+0x4f/0x70 [ 145.183925] [<ffffffffa2b2a5b9>] kernfs_fop_write+0x149/0x180 [ 145.189761] [<ffffffffa2a99248>] __vfs_write+0x18/0x40 [ 145.194982] [<ffffffffa2a9a412>] vfs_write+0xb2/0x1a0 [ 145.200122] [<ffffffffa2a9a732>] SyS_write+0x52/0xa0 [ 145.205177] [<ffffffffa2ff4d97>] entry_SYSCALL_64_fastpath+0x12/0x17 This can be even triggered manually by changing /sys/module/zswap/parameters/compressor multiple times. Fix this issue by making unregister APIs symmetric to the register so there are no surprises. Fixes: 47e627bc8c9a ("[PATCH] hotplug: Allow modules to use the cpu hotplug notifiers even if !CONFIG_HOTPLUG_CPU") Reported-and-tested-by: Yu Zhao <yuzhao@google.com> Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: linux-mm@kvack.org Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dan Streetman <ddstreet@ieee.org> Link: http://lkml.kernel.org/r/20161207135438.4310-1-mhocko@kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 777c6e0daebb3fcefbbd6f620410a946b07ef6d0 upstream.

Yu Zhao has noticed that __unregister_cpu_notifier only unregisters its
notifiers when HOTPLUG_CPU=y while the registration might succeed even
when HOTPLUG_CPU=n if MODULE is enabled. This means that e.g. zswap
might keep a stale notifier on the list on the manual clean up during
the pool tear down and thus corrupt the list. Resulting in the following

[  144.964346] BUG: unable to handle kernel paging request at ffff880658a2be78
[  144.971337] IP: [<ffffffffa290b00b>] raw_notifier_chain_register+0x1b/0x40
<snipped>
[  145.122628] Call Trace:
[  145.125086]  [<ffffffffa28e5cf8>] __register_cpu_notifier+0x18/0x20
[  145.131350]  [<ffffffffa2a5dd73>] zswap_pool_create+0x273/0x400
[  145.137268]  [<ffffffffa2a5e0fc>] __zswap_param_set+0x1fc/0x300
[  145.143188]  [<ffffffffa2944c1d>] ? trace_hardirqs_on+0xd/0x10
[  145.149018]  [<ffffffffa2908798>] ? kernel_param_lock+0x28/0x30
[  145.154940]  [<ffffffffa2a3e8cf>] ? __might_fault+0x4f/0xa0
[  145.160511]  [<ffffffffa2a5e237>] zswap_compressor_param_set+0x17/0x20
[  145.167035]  [<ffffffffa2908d3c>] param_attr_store+0x5c/0xb0
[  145.172694]  [<ffffffffa290848d>] module_attr_store+0x1d/0x30
[  145.178443]  [<ffffffffa2b2b41f>] sysfs_kf_write+0x4f/0x70
[  145.183925]  [<ffffffffa2b2a5b9>] kernfs_fop_write+0x149/0x180
[  145.189761]  [<ffffffffa2a99248>] __vfs_write+0x18/0x40
[  145.194982]  [<ffffffffa2a9a412>] vfs_write+0xb2/0x1a0
[  145.200122]  [<ffffffffa2a9a732>] SyS_write+0x52/0xa0
[  145.205177]  [<ffffffffa2ff4d97>] entry_SYSCALL_64_fastpath+0x12/0x17

This can be even triggered manually by changing
/sys/module/zswap/parameters/compressor multiple times.

Fix this issue by making unregister APIs symmetric to the register so
there are no surprises.

Fixes: 47e627bc8c9a ("[PATCH] hotplug: Allow modules to use the cpu hotplug notifiers even if !CONFIG_HOTPLUG_CPU")
Reported-and-tested-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Link: http://lkml.kernel.org/r/20161207135438.4310-1-mhocko@kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
locking/rtmutex: Use READ_ONCE() in rt_mutex_owner() 2016-12-15T16:49:22+00:00 Thomas Gleixner tglx@linutronix.de 2016-11-30T21:04:42+00:00 c6a5bf4cda12e4a3c097036ce7044ee65e4cf6d9 commit 1be5d4fa0af34fb7bafa205aeb59f5c7cc7a089d upstream. While debugging the rtmutex unlock vs. dequeue race Will suggested to use READ_ONCE() in rt_mutex_owner() as it might race against the cmpxchg_release() in unlock_rt_mutex_safe(). Will: "It's a minor thing which will most likely not matter in practice" Careful search did not unearth an actual problem in todays code, but it's better to be safe than surprised. Suggested-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sebastian Siewior <bigeasy@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Link: http://lkml.kernel.org/r/20161130210030.431379999@linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 1be5d4fa0af34fb7bafa205aeb59f5c7cc7a089d upstream.

While debugging the rtmutex unlock vs. dequeue race Will suggested to use
READ_ONCE() in rt_mutex_owner() as it might race against the
cmpxchg_release() in unlock_rt_mutex_safe().

Will: "It's a minor thing which will most likely not matter in practice"

Careful search did not unearth an actual problem in todays code, but it's
better to be safe than surprised.

Suggested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David Daney <ddaney@caviumnetworks.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20161130210030.431379999@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
locking/rtmutex: Prevent dequeue vs. unlock race 2016-12-15T16:49:22+00:00 Thomas Gleixner tglx@linutronix.de 2016-11-30T21:04:41+00:00 b27d9147f24a501d632916964f77c1221246fae9 commit dbb26055defd03d59f678cb5f2c992abe05b064a upstream. David reported a futex/rtmutex state corruption. It's caused by the following problem: CPU0 CPU1 CPU2 l->owner=T1 rt_mutex_lock(l) lock(l->wait_lock) l->owner = T1 | HAS_WAITERS; enqueue(T2) boost() unlock(l->wait_lock) schedule() rt_mutex_lock(l) lock(l->wait_lock) l->owner = T1 | HAS_WAITERS; enqueue(T3) boost() unlock(l->wait_lock) schedule() signal(->T2) signal(->T3) lock(l->wait_lock) dequeue(T2) deboost() unlock(l->wait_lock) lock(l->wait_lock) dequeue(T3) ===> wait list is now empty deboost() unlock(l->wait_lock) lock(l->wait_lock) fixup_rt_mutex_waiters() if (wait_list_empty(l)) { owner = l->owner & ~HAS_WAITERS; l->owner = owner ==> l->owner = T1 } lock(l->wait_lock) rt_mutex_unlock(l) fixup_rt_mutex_waiters() if (wait_list_empty(l)) { owner = l->owner & ~HAS_WAITERS; cmpxchg(l->owner, T1, NULL) ===> Success (l->owner = NULL) l->owner = owner ==> l->owner = T1 } That means the problem is caused by fixup_rt_mutex_waiters() which does the RMW to clear the waiters bit unconditionally when there are no waiters in the rtmutexes rbtree. This can be fatal: A concurrent unlock can release the rtmutex in the fastpath because the waiters bit is not set. If the cmpxchg() gets in the middle of the RMW operation then the previous owner, which just unlocked the rtmutex is set as the owner again when the write takes place after the successfull cmpxchg(). The solution is rather trivial: verify that the owner member of the rtmutex has the waiters bit set before clearing it. This does not require a cmpxchg() or other atomic operations because the waiters bit can only be set and cleared with the rtmutex wait_lock held. It's also safe against the fast path unlock attempt. The unlock attempt via cmpxchg() will either see the bit set and take the slowpath or see the bit cleared and release it atomically in the fastpath. It's remarkable that the test program provided by David triggers on ARM64 and MIPS64 really quick, but it refuses to reproduce on x86-64, while the problem exists there as well. That refusal might explain that this got not discovered earlier despite the bug existing from day one of the rtmutex implementation more than 10 years ago. Thanks to David for meticulously instrumenting the code and providing the information which allowed to decode this subtle problem. Reported-by: David Daney <ddaney@caviumnetworks.com> Tested-by: David Daney <david.daney@cavium.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sebastian Siewior <bigeasy@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Fixes: 23f78d4a03c5 ("[PATCH] pi-futex: rt mutex core") Link: http://lkml.kernel.org/r/20161130210030.351136722@linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit dbb26055defd03d59f678cb5f2c992abe05b064a upstream.

David reported a futex/rtmutex state corruption. It's caused by the
following problem:

CPU0		CPU1		CPU2

l->owner=T1
		rt_mutex_lock(l)
		lock(l->wait_lock)
		l->owner = T1 | HAS_WAITERS;
		enqueue(T2)
		boost()
		  unlock(l->wait_lock)
		schedule()

				rt_mutex_lock(l)
				lock(l->wait_lock)
				l->owner = T1 | HAS_WAITERS;
				enqueue(T3)
				boost()
				  unlock(l->wait_lock)
				schedule()
		signal(->T2)	signal(->T3)
		lock(l->wait_lock)
		dequeue(T2)
		deboost()
		  unlock(l->wait_lock)
				lock(l->wait_lock)
				dequeue(T3)
				  ===> wait list is now empty
				deboost()
				 unlock(l->wait_lock)
		lock(l->wait_lock)
		fixup_rt_mutex_waiters()
		  if (wait_list_empty(l)) {
		    owner = l->owner & ~HAS_WAITERS;
		    l->owner = owner
		     ==> l->owner = T1
		  }

				lock(l->wait_lock)
rt_mutex_unlock(l)		fixup_rt_mutex_waiters()
				  if (wait_list_empty(l)) {
				    owner = l->owner & ~HAS_WAITERS;
cmpxchg(l->owner, T1, NULL)
 ===> Success (l->owner = NULL)
				    l->owner = owner
				     ==> l->owner = T1
				  }

That means the problem is caused by fixup_rt_mutex_waiters() which does the
RMW to clear the waiters bit unconditionally when there are no waiters in
the rtmutexes rbtree.

This can be fatal: A concurrent unlock can release the rtmutex in the
fastpath because the waiters bit is not set. If the cmpxchg() gets in the
middle of the RMW operation then the previous owner, which just unlocked
the rtmutex is set as the owner again when the write takes place after the
successfull cmpxchg().

The solution is rather trivial: verify that the owner member of the rtmutex
has the waiters bit set before clearing it. This does not require a
cmpxchg() or other atomic operations because the waiters bit can only be
set and cleared with the rtmutex wait_lock held. It's also safe against the
fast path unlock attempt. The unlock attempt via cmpxchg() will either see
the bit set and take the slowpath or see the bit cleared and release it
atomically in the fastpath.

It's remarkable that the test program provided by David triggers on ARM64
and MIPS64 really quick, but it refuses to reproduce on x86-64, while the
problem exists there as well. That refusal might explain that this got not
discovered earlier despite the bug existing from day one of the rtmutex
implementation more than 10 years ago.

Thanks to David for meticulously instrumenting the code and providing the
information which allowed to decode this subtle problem.

Reported-by: David Daney <ddaney@caviumnetworks.com>
Tested-by: David Daney <david.daney@cavium.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Fixes: 23f78d4a03c5 ("[PATCH] pi-futex: rt mutex core")
Link: http://lkml.kernel.org/r/20161130210030.351136722@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
rcu: Fix soft lockup for rcu_nocb_kthread 2016-12-08T06:15:24+00:00 Ding Tianhong dingtianhong@huawei.com 2016-06-15T07:27:36+00:00 dfb704f96cd190239e7b86b09810a136cf25506e commit bedc1969150d480c462cdac320fa944b694a7162 upstream. Carrying out the following steps results in a softlockup in the RCU callback-offload (rcuo) kthreads: 1. Connect to ixgbevf, and set the speed to 10Gb/s. 2. Use ifconfig to bring the nic up and down repeatedly. [ 317.005148] IPv6: ADDRCONF(NETDEV_CHANGE): eth2: link becomes ready [ 368.106005] BUG: soft lockup - CPU#1 stuck for 22s! [rcuos/1:15] [ 368.106005] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 368.106005] task: ffff88057dd8a220 ti: ffff88057dd9c000 task.ti: ffff88057dd9c000 [ 368.106005] RIP: 0010:[<ffffffff81579e04>] [<ffffffff81579e04>] fib_table_lookup+0x14/0x390 [ 368.106005] RSP: 0018:ffff88061fc83ce8 EFLAGS: 00000286 [ 368.106005] RAX: 0000000000000001 RBX: 00000000020155c0 RCX: 0000000000000001 [ 368.106005] RDX: ffff88061fc83d50 RSI: ffff88061fc83d70 RDI: ffff880036d11a00 [ 368.106005] RBP: ffff88061fc83d08 R08: 0000000000000001 R09: 0000000000000000 [ 368.106005] R10: ffff880036d11a00 R11: ffffffff819e0900 R12: ffff88061fc83c58 [ 368.106005] R13: ffffffff816154dd R14: ffff88061fc83d08 R15: 00000000020155c0 [ 368.106005] FS: 0000000000000000(0000) GS:ffff88061fc80000(0000) knlGS:0000000000000000 [ 368.106005] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 368.106005] CR2: 00007f8c2aee9c40 CR3: 000000057b222000 CR4: 00000000000407e0 [ 368.106005] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 368.106005] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 [ 368.106005] Stack: [ 368.106005] 00000000010000c0 ffff88057b766000 ffff8802e380b000 ffff88057af03e00 [ 368.106005] ffff88061fc83dc0 ffffffff815349a6 ffff88061fc83d40 ffffffff814ee146 [ 368.106005] ffff8802e380af00 00000000e380af00 ffffffff819e0900 020155c0010000c0 [ 368.106005] Call Trace: [ 368.106005] <IRQ> [ 368.106005] [ 368.106005] [<ffffffff815349a6>] ip_route_input_noref+0x516/0xbd0 [ 368.106005] [<ffffffff814ee146>] ? skb_release_data+0xd6/0x110 [ 368.106005] [<ffffffff814ee20a>] ? kfree_skb+0x3a/0xa0 [ 368.106005] [<ffffffff8153698f>] ip_rcv_finish+0x29f/0x350 [ 368.106005] [<ffffffff81537034>] ip_rcv+0x234/0x380 [ 368.106005] [<ffffffff814fd656>] __netif_receive_skb_core+0x676/0x870 [ 368.106005] [<ffffffff814fd868>] __netif_receive_skb+0x18/0x60 [ 368.106005] [<ffffffff814fe4de>] process_backlog+0xae/0x180 [ 368.106005] [<ffffffff814fdcb2>] net_rx_action+0x152/0x240 [ 368.106005] [<ffffffff81077b3f>] __do_softirq+0xef/0x280 [ 368.106005] [<ffffffff8161619c>] call_softirq+0x1c/0x30 [ 368.106005] <EOI> [ 368.106005] [ 368.106005] [<ffffffff81015d95>] do_softirq+0x65/0xa0 [ 368.106005] [<ffffffff81077174>] local_bh_enable+0x94/0xa0 [ 368.106005] [<ffffffff81114922>] rcu_nocb_kthread+0x232/0x370 [ 368.106005] [<ffffffff81098250>] ? wake_up_bit+0x30/0x30 [ 368.106005] [<ffffffff811146f0>] ? rcu_start_gp+0x40/0x40 [ 368.106005] [<ffffffff8109728f>] kthread+0xcf/0xe0 [ 368.106005] [<ffffffff810971c0>] ? kthread_create_on_node+0x140/0x140 [ 368.106005] [<ffffffff816147d8>] ret_from_fork+0x58/0x90 [ 368.106005] [<ffffffff810971c0>] ? kthread_create_on_node+0x140/0x140 ==================================cut here============================== It turns out that the rcuos callback-offload kthread is busy processing a very large quantity of RCU callbacks, and it is not reliquishing the CPU while doing so. This commit therefore adds an cond_resched_rcu_qs() within the loop to allow other tasks to run. Signed-off-by: Ding Tianhong <dingtianhong@huawei.com> [ paulmck: Substituted cond_resched_rcu_qs for cond_resched. ] Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Dhaval Giani <dhaval.giani@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit bedc1969150d480c462cdac320fa944b694a7162 upstream.

Carrying out the following steps results in a softlockup in the
RCU callback-offload (rcuo) kthreads:

1. Connect to ixgbevf, and set the speed to 10Gb/s.
2. Use ifconfig to bring the nic up and down repeatedly.

[  317.005148] IPv6: ADDRCONF(NETDEV_CHANGE): eth2: link becomes ready
[  368.106005] BUG: soft lockup - CPU#1 stuck for 22s! [rcuos/1:15]
[  368.106005] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  368.106005] task: ffff88057dd8a220 ti: ffff88057dd9c000 task.ti: ffff88057dd9c000
[  368.106005] RIP: 0010:[<ffffffff81579e04>]  [<ffffffff81579e04>] fib_table_lookup+0x14/0x390
[  368.106005] RSP: 0018:ffff88061fc83ce8  EFLAGS: 00000286
[  368.106005] RAX: 0000000000000001 RBX: 00000000020155c0 RCX: 0000000000000001
[  368.106005] RDX: ffff88061fc83d50 RSI: ffff88061fc83d70 RDI: ffff880036d11a00
[  368.106005] RBP: ffff88061fc83d08 R08: 0000000000000001 R09: 0000000000000000
[  368.106005] R10: ffff880036d11a00 R11: ffffffff819e0900 R12: ffff88061fc83c58
[  368.106005] R13: ffffffff816154dd R14: ffff88061fc83d08 R15: 00000000020155c0
[  368.106005] FS:  0000000000000000(0000) GS:ffff88061fc80000(0000) knlGS:0000000000000000
[  368.106005] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  368.106005] CR2: 00007f8c2aee9c40 CR3: 000000057b222000 CR4: 00000000000407e0
[  368.106005] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  368.106005] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  368.106005] Stack:
[  368.106005]  00000000010000c0 ffff88057b766000 ffff8802e380b000 ffff88057af03e00
[  368.106005]  ffff88061fc83dc0 ffffffff815349a6 ffff88061fc83d40 ffffffff814ee146
[  368.106005]  ffff8802e380af00 00000000e380af00 ffffffff819e0900 020155c0010000c0
[  368.106005] Call Trace:
[  368.106005]  <IRQ>
[  368.106005]
[  368.106005]  [<ffffffff815349a6>] ip_route_input_noref+0x516/0xbd0
[  368.106005]  [<ffffffff814ee146>] ? skb_release_data+0xd6/0x110
[  368.106005]  [<ffffffff814ee20a>] ? kfree_skb+0x3a/0xa0
[  368.106005]  [<ffffffff8153698f>] ip_rcv_finish+0x29f/0x350
[  368.106005]  [<ffffffff81537034>] ip_rcv+0x234/0x380
[  368.106005]  [<ffffffff814fd656>] __netif_receive_skb_core+0x676/0x870
[  368.106005]  [<ffffffff814fd868>] __netif_receive_skb+0x18/0x60
[  368.106005]  [<ffffffff814fe4de>] process_backlog+0xae/0x180
[  368.106005]  [<ffffffff814fdcb2>] net_rx_action+0x152/0x240
[  368.106005]  [<ffffffff81077b3f>] __do_softirq+0xef/0x280
[  368.106005]  [<ffffffff8161619c>] call_softirq+0x1c/0x30
[  368.106005]  <EOI>
[  368.106005]
[  368.106005]  [<ffffffff81015d95>] do_softirq+0x65/0xa0
[  368.106005]  [<ffffffff81077174>] local_bh_enable+0x94/0xa0
[  368.106005]  [<ffffffff81114922>] rcu_nocb_kthread+0x232/0x370
[  368.106005]  [<ffffffff81098250>] ? wake_up_bit+0x30/0x30
[  368.106005]  [<ffffffff811146f0>] ? rcu_start_gp+0x40/0x40
[  368.106005]  [<ffffffff8109728f>] kthread+0xcf/0xe0
[  368.106005]  [<ffffffff810971c0>] ? kthread_create_on_node+0x140/0x140
[  368.106005]  [<ffffffff816147d8>] ret_from_fork+0x58/0x90
[  368.106005]  [<ffffffff810971c0>] ? kthread_create_on_node+0x140/0x140

==================================cut here==============================

It turns out that the rcuos callback-offload kthread is busy processing
a very large quantity of RCU callbacks, and it is not reliquishing the
CPU while doing so.  This commit therefore adds an cond_resched_rcu_qs()
within the loop to allow other tasks to run.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
[ paulmck: Substituted cond_resched_rcu_qs for cond_resched. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Dhaval Giani <dhaval.giani@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
PM / sleep: fix device reference leak in test_suspend 2016-11-26T08:54:53+00:00 Johan Hovold johan@kernel.org 2016-11-01T10:49:56+00:00 469fcbcb84d809ec05567d51f4fb664b894517e0 commit ceb75787bc75d0a7b88519ab8a68067ac690f55a upstream. Make sure to drop the reference taken by class_find_device() after opening the RTC device. Fixes: 77437fd4e61f (pm: boot time suspend selftest) Signed-off-by: Johan Hovold <johan@kernel.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit ceb75787bc75d0a7b88519ab8a68067ac690f55a upstream.

Make sure to drop the reference taken by class_find_device() after
opening the RTC device.

Fixes: 77437fd4e61f (pm: boot time suspend selftest)
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>