linux-toradex.git/kernel/hung_task.c, branch v3.15-rc6

kernel: audit/fix non-modular users of module_init in core code

2014-04-03T23:21:07+00:00

Code that is obj-y (always built-in) or dependent on a bool Kconfig
(built-in or absent) can never be modular.  So using module_init as an
alias for __initcall can be somewhat misleading.

Fix these up now, so that we can relocate module_init from init.h into
module.h in the future.  If we don't do this, we'd have to add module.h
to obviously non-modular code, and that would be a worse thing.

The audit targets the following module_init users for change:
 kernel/user.c                  obj-y
 kernel/kexec.c                 bool KEXEC (one instance per arch)
 kernel/profile.c               bool PROFILING
 kernel/hung_task.c             bool DETECT_HUNG_TASK
 kernel/sched/stats.c           bool SCHEDSTATS
 kernel/user_namespace.c        bool USER_NS

Note that direct use of __initcall is discouraged, vs.  one of the
priority categorized subgroups.  As __initcall gets mapped onto
device_initcall, our use of subsys_initcall (which makes sense for these
files) will thus change this registration from level 6-device to level
4-subsys (i.e.  slightly earlier).  However no observable impact of that
difference has been observed during testing.

Also, two instances of missing ";" at EOL are fixed in kexec.

Signed-off-by: Paul Gortmaker 
Cc: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: Eric Biederman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

hung_task: Display every hung task warning

2014-01-25T11:13:33+00:00

When khungtaskd detects hung tasks, it prints out
backtraces from a number of those tasks.

Limiting the number of backtraces being printed
out can result in the user not seeing the information
necessary to debug the issue. The hung_task_warnings
sysctl controls this feature.

This patch makes it possible for hung_task_warnings
to accept a special value to print an unlimited
number of backtraces when khungtaskd detects hung
tasks.

The special value is -1. To use this value it is
necessary to change types from ulong to int.

Signed-off-by: Aaron Tomlin 
Reviewed-by: Rik van Riel 
Acked-by: David Rientjes 
Cc: oleg@redhat.com
Link: http://lkml.kernel.org/r/1390239253-24030-3-git-send-email-atomlin@redhat.com
[ Build warning fix. ]
Signed-off-by: Ingo Molnar

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2013-11-15T04:51:36+00:00

Pull KVM changes from Paolo Bonzini:
 "Here are the 3.13 KVM changes.  There was a lot of work on the PPC
  side: the HV and emulation flavors can now coexist in a single kernel
  is probably the most interesting change from a user point of view.

  On the x86 side there are nested virtualization improvements and a few
  bugfixes.

  ARM got transparent huge page support, improved overcommit, and
  support for big endian guests.

  Finally, there is a new interface to connect KVM with VFIO.  This
  helps with devices that use NoSnoop PCI transactions, letting the
  driver in the guest execute WBINVD instructions.  This includes some
  nVidia cards on Windows, that fail to start without these patches and
  the corresponding userspace changes"

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (146 commits)
  kvm, vmx: Fix lazy FPU on nested guest
  arm/arm64: KVM: PSCI: propagate caller endianness to the incoming vcpu
  arm/arm64: KVM: MMIO support for BE guest
  kvm, cpuid: Fix sparse warning
  kvm: Delete prototype for non-existent function kvm_check_iopl
  kvm: Delete prototype for non-existent function complete_pio
  hung_task: add method to reset detector
  pvclock: detect watchdog reset at pvclock read
  kvm: optimize out smp_mb after srcu_read_unlock
  srcu: API for barrier after srcu read unlock
  KVM: remove vm mmap method
  KVM: IOMMU: hva align mapping page size
  KVM: x86: trace cpuid emulation when called from emulator
  KVM: emulator: cleanup decode_register_operand() a bit
  KVM: emulator: check rex prefix inside decode_register()
  KVM: x86: fix emulation of "movzbl %bpl, %eax"
  kvm_host: typo fix
  KVM: x86: emulate SAHF instruction
  MAINTAINERS: add tree for kvm.git
  Documentation/kvm: add a 00-INDEX file
  ...

hung_task: add method to reset detector

2013-11-06T07:49:02+00:00

In certain occasions it is possible for a hung task detector
positive to be false: continuation from a paused VM, for example.

Add a method to reset detection, similar as is done
with other kernel watchdogs.

Acked-by: Don Zickus 
Acked-by: Paolo Bonzini 
Signed-off-by: Marcelo Tosatti 
Signed-off-by: Gleb Natapov

hung_task debugging: Add tracepoint to report the hang

2013-10-31T10:16:18+00:00

Currently check_hung_task() prints a warning if it detects the
problem, but it is not convenient to watch the system logs if
user-space wants to be notified about the hang.

Add the new trace_sched_process_hang() into check_hung_task(),
this way a user-space monitor can easily wait for the hang and
potentially resolve a problem.

Signed-off-by: Oleg Nesterov 
Cc: Dave Sullivan 
Cc: Peter Zijlstra 
Cc: Steven Rostedt 
Link: http://lkml.kernel.org/r/20131019161828.GA7439@redhat.com
Signed-off-by: Ingo Molnar

hung_task: Change sysctl_hung_task_check_count to 'int'

2013-09-23T09:10:49+00:00

As 'sysctl_hung_task_check_count' is 'unsigned long' when this
value is assigned to max_count in check_hung_uninterruptible_tasks(),
it's truncated to 'int' type.

This causes a minor artifact: if we write 2^32 to sysctl.hung_task_check_count,
hung task detection will be effectively disabled.

With this fix, it will still truncate the user input to 32 bits, but
reading sysctl.hung_task_check_count reflects the actual truncated value.

Signed-off-by: Li Zefan 
Acked-by: Ingo Molnar 
Link: http://lkml.kernel.org/r/523FFF4E.9050401@huawei.com
Signed-off-by: Ingo Molnar

hung_task debugging: Print more info when reporting the problem

2013-08-02T09:02:42+00:00

printk(KERN_ERR) from check_hung_task() likely means we have a bug,
but unlike BUG_ON()/WARN_ON ()it doesn't show the kernel version,
this complicates the bug-reports investigation.

Add the additional pr_err() to print tainted/release/version
like dump_stack_print_info() does, the output becomes:

        INFO: task perl:504 blocked for more than 2 seconds.
	      Not tainted 3.11.0-rc1-10367-g136bb46-dirty #1763
        "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
        ...

While at it, turn the old printk's into pr_err().

Signed-off-by: Oleg Nesterov 
Cc: ahecox@redhat.com
Cc: Christopher Williams 
Cc: dwysocha@redhat.com
Cc: gavin@redhat.com
Cc: Mandeep Singh Baines 
Cc: nshi@redhat.com
Cc: Linus Torvalds 
Cc: Andrew Morton 
Cc: Peter Zijlstra 
Link: http://lkml.kernel.org/r/20130801165941.GA17544@redhat.com
Signed-off-by: Ingo Molnar

hung task debugging: Inject NMI when hung and going to panic

2012-04-25T10:39:25+00:00

Send an NMI to all CPUs when a hung task is detected and the hung
task code is configured to panic. This gives us a fairly uptodate
snapshot of all CPUs in the system.

This lets us get stack trace of all CPUs which makes life easier
trying to debug a deadlock, and the NMI doesn't change anything
since the next step is a kernel panic.

Signed-off-by: Sasha Levin 
Cc: Linus Torvalds 
Cc: Andrew Morton 
Link: http://lkml.kernel.org/r/1331848040-1676-1-git-send-email-levinsasha928@gmail.com
[ extended the changelog a bit ]
Signed-off-by: Ingo Molnar

hung_task: fix the broken rcu_lock_break() logic

2012-03-05T23:49:42+00:00

check_hung_uninterruptible_tasks()->rcu_lock_break() introduced by
"softlockup: check all tasks in hung_task" commit ce9dbe24 looks
absolutely wrong.

	- rcu_lock_break() does put_task_struct(). If the task has exited
	  it is not safe to even read its ->state, nothing protects this
	  task_struct.

	- The TASK_DEAD checks are wrong too. Contrary to the comment, we
	  can't use it to check if the task was unhashed. It can be unhashed
	  without TASK_DEAD, or it can be valid with TASK_DEAD.

	  For example, an autoreaping task can do release_task(current)
	  long before it sets TASK_DEAD in do_exit().

	  Or, a zombie task can have ->state == TASK_DEAD but release_task()
	  was not called, and in this case we must not break the loop.

Change this code to check pid_alive() instead, and do this before we drop
the reference to the task_struct.

Note: while_each_thread() under rcu_read_lock() is not really safe, it can
livelock.  This will be fixed later, but fortunately in this case the
"max_count" logic saves us anyway.

Signed-off-by: Oleg Nesterov 
Acked-by: Frederic Weisbecker 
Acked-by: Mandeep Singh Baines 
Acked-by: Paul E. McKenney 
Cc: Tetsuo Handa 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

hung_task: fix false positive during vfork

2012-01-04T00:14:32+00:00

vfork parent uninterruptibly and unkillably waits for its child to
exec/exit. This wait is of unbounded length. Ignore such waits
in the hung_task detector.

Signed-off-by: Mandeep Singh Baines 
Reported-by: Sasha Levin 
LKML-Reference: <1325344394.28904.43.camel@lappy>
Cc: Linus Torvalds 
Cc: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: Andrew Morton 
Cc: John Kacur 
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds