linux-toradex.git/include/linux/hrtimer.h, branch v6.6-rc5

timekeeping: Distangle resume and clock-was-set events

2021-08-10T15:57:23+00:00

Resuming timekeeping is a clock-was-set event and uses the clock-was-set
notification mechanism. This is in the way of making the clock-was-set
update for hrtimers selective so unnecessary IPIs are avoided when a CPU
base does not have timers queued which are affected by the clock setting.

Distangle it by invoking hrtimer_resume() on each unfreezing CPU and invoke
the new timerfd_resume() function from timekeeping_resume() which is the
only place where this is needed.

Rename hrtimer_resume() to hrtimer_resume_local() to reflect the change.

With this the clock_was_set*() functions are not longer required to IPI all
CPUs unconditionally and can get some smarts to avoid them.

Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210713135158.488853478@linutronix.de

timerfd: Provide timerfd_resume()

2021-08-10T15:57:22+00:00

Resuming timekeeping is a clock-was-set event and uses the clock-was-set
notification mechanism. This is in the way of making the clock-was-set
update for hrtimers selective so unnecessary IPIs are avoided when a CPU
base does not have timers queued which are affected by the clock setting.

Provide a seperate timerfd_resume() interface so the resume logic and the
clock-was-set mechanism can be distangled in the core code.

Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210713135158.395287410@linutronix.de

hrtimer: Ensure timerfd notification for HIGHRES=n

2021-08-10T15:57:22+00:00

If high resolution timers are disabled the timerfd notification about a
clock was set event is not happening for all cases which use
clock_was_set_delayed() because that's a NOP for HIGHRES=n, which is wrong.

Make clock_was_set_delayed() unconditially available to fix that.

Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210713135158.196661266@linutronix.de

hrtimer: Fix kernel-doc markups

2020-11-16T14:20:01+00:00

The hrtimer_get_remaining() markup is documenting, instead,
__hrtimer_get_remaining(), as it is placed at the C file.

In order to properly document it, a kernel-doc markup is needed together
with the function prototype. So, add a new one, while preserving the
existing one, just fixing the function name.

The hrtimer_is_queued prototype has a typo: it is using
'=' instead of '-' to split: identifier - description
as required by kernel-doc markup.

Signed-off-by: Mauro Carvalho Chehab 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/9dc87808c2fd07b7e050bafcd033c5ef05808fea.1605521731.git.mchehab+huawei@kernel.org

locking/seqlock, headers: Untangle the spaghetti monster

2020-08-06T14:13:13+00:00

By using lockdep_assert_*() from seqlock.h, the spaghetti monster
attacked.

Attack back by reducing seqlock.h dependencies from two key high level headers:

 - :               -Remove 
 - :                  -Remove 
 - :                 +Add    

The price was to add it to sched.h ...

Core header fallout, we add direct header dependencies instead of gaining them
parasitically from higher level headers:

 - :  +Add 
 - :               +Add 
 - :                 +Add 
 - :               +Add 
 - :                 +Add 
 - :             +Add 

Arch headers fallout:

 - PARISC: :           +Add 
 - SH:     :              +Add 
 - SPARC:  :        +Add 
 - SPARC:  :            +Add , 
                                    -Remove 
 - X86:    :          +Add 
                                    -Remove 

There's also a bunch of parasitic header dependency fallout in .c files, not listed
separately.

[ mingo: Extended the changelog, split up & fixed the original patch. ]

Co-developed-by: Ingo Molnar 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Link: https://lore.kernel.org/r/20200804133438.GK2674@hirez.programming.kicks-ass.net

hrtimer: Use sequence counter with associated raw spinlock

2020-07-29T14:14:29+00:00

A sequence counter write side critical section must be protected by some
form of locking to serialize writers. A plain seqcount_t does not
contain the information of which lock must be held when entering a write
side critical section.

Use the new seqcount_raw_spinlock_t data type, which allows to associate
a raw spinlock with the sequence counter. This enables lockdep to verify
that the raw spinlock used for writer serialization is held when the
write side critical section is entered.

If lockdep is disabled this lock association is compiled out and has
neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20200720155530.1173732-25-a.darwish@linutronix.de

hrtimers: Prepare hrtimer_nanosleep() for time namespaces

2020-01-14T11:20:55+00:00

clock_nanosleep() accepts absolute values of expiration time when
TIMER_ABSTIME flag is set. This absolute value is inside the task's
time namespace, and has to be converted to the host's time.

There is timens_ktime_to_host() helper for converting time, but
it accepts ktime argument.

As a preparation, make hrtimer_nanosleep() accept a clock value in ktime
instead of timespec64.

Co-developed-by: Dmitry Safonov 
Signed-off-by: Andrei Vagin 
Signed-off-by: Dmitry Safonov 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20191112012724.250792-17-dima@arista.com

hrtimer: Annotate lockless access to timer->state

2019-11-06T22:18:31+00:00

syzbot reported various data-race caused by hrtimer_is_queued() reading
timer->state. A READ_ONCE() is required there to silence the warning.

Also add the corresponding WRITE_ONCE() when timer->state is set.

In remove_hrtimer() the hrtimer_is_queued() helper is open coded to avoid
loading timer->state twice.

KCSAN reported these cases:

BUG: KCSAN: data-race in __remove_hrtimer / tcp_pacing_check

write to 0xffff8880b2a7d388 of 1 bytes by interrupt on cpu 0:
 __remove_hrtimer+0x52/0x130 kernel/time/hrtimer.c:991
 __run_hrtimer kernel/time/hrtimer.c:1496 [inline]
 __hrtimer_run_queues+0x250/0x600 kernel/time/hrtimer.c:1576
 hrtimer_run_softirq+0x10e/0x150 kernel/time/hrtimer.c:1593
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 run_ksoftirqd+0x46/0x60 kernel/softirq.c:603
 smpboot_thread_fn+0x37d/0x4a0 kernel/smpboot.c:165
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8880b2a7d388 of 1 bytes by task 24652 on cpu 1:
 tcp_pacing_check net/ipv4/tcp_output.c:2235 [inline]
 tcp_pacing_check+0xba/0x130 net/ipv4/tcp_output.c:2225
 tcp_xmit_retransmit_queue+0x32c/0x5a0 net/ipv4/tcp_output.c:3044
 tcp_xmit_recovery+0x7c/0x120 net/ipv4/tcp_input.c:3558
 tcp_ack+0x17b6/0x3170 net/ipv4/tcp_input.c:3717
 tcp_rcv_established+0x37e/0xf50 net/ipv4/tcp_input.c:5696
 tcp_v4_do_rcv+0x381/0x4e0 net/ipv4/tcp_ipv4.c:1561
 sk_backlog_rcv include/net/sock.h:945 [inline]
 __release_sock+0x135/0x1e0 net/core/sock.c:2435
 release_sock+0x61/0x160 net/core/sock.c:2951
 sk_stream_wait_memory+0x3d7/0x7c0 net/core/stream.c:145
 tcp_sendmsg_locked+0xb47/0x1f30 net/ipv4/tcp.c:1393
 tcp_sendmsg+0x39/0x60 net/ipv4/tcp.c:1434
 inet_sendmsg+0x6d/0x90 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:637 [inline]
 sock_sendmsg+0x9f/0xc0 net/socket.c:657

BUG: KCSAN: data-race in __remove_hrtimer / __tcp_ack_snd_check

write to 0xffff8880a3a65588 of 1 bytes by interrupt on cpu 0:
 __remove_hrtimer+0x52/0x130 kernel/time/hrtimer.c:991
 __run_hrtimer kernel/time/hrtimer.c:1496 [inline]
 __hrtimer_run_queues+0x250/0x600 kernel/time/hrtimer.c:1576
 hrtimer_run_softirq+0x10e/0x150 kernel/time/hrtimer.c:1593
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830

read to 0xffff8880a3a65588 of 1 bytes by task 22891 on cpu 1:
 __tcp_ack_snd_check+0x415/0x4f0 net/ipv4/tcp_input.c:5265
 tcp_ack_snd_check net/ipv4/tcp_input.c:5287 [inline]
 tcp_rcv_established+0x750/0xf50 net/ipv4/tcp_input.c:5708
 tcp_v4_do_rcv+0x381/0x4e0 net/ipv4/tcp_ipv4.c:1561
 sk_backlog_rcv include/net/sock.h:945 [inline]
 __release_sock+0x135/0x1e0 net/core/sock.c:2435
 release_sock+0x61/0x160 net/core/sock.c:2951
 sk_stream_wait_memory+0x3d7/0x7c0 net/core/stream.c:145
 tcp_sendmsg_locked+0xb47/0x1f30 net/ipv4/tcp.c:1393
 tcp_sendmsg+0x39/0x60 net/ipv4/tcp.c:1434
 inet_sendmsg+0x6d/0x90 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:637 [inline]
 sock_sendmsg+0x9f/0xc0 net/socket.c:657
 __sys_sendto+0x21f/0x320 net/socket.c:1952
 __do_sys_sendto net/socket.c:1964 [inline]
 __se_sys_sendto net/socket.c:1960 [inline]
 __x64_sys_sendto+0x89/0xb0 net/socket.c:1960
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24652 Comm: syz-executor.3 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

[ tglx: Added comments ]

Reported-by: syzbot 
Signed-off-by: Eric Dumazet 
Signed-off-by: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20191106174804.74723-1-edumazet@google.com

hrtimer: Add kernel doc annotation for HRTIMER_MODE_HARD

2019-08-28T11:01:25+00:00

Add kernel doc annotation for HRTIMER_MODE_HARD.

Fixes: ae6683d815895 ("hrtimer: Introduce HARD expiry mode")
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20190823113845.12125-2-bigeasy@linutronix.de

hrtimer: Prepare support for PREEMPT_RT

2019-08-01T18:51:22+00:00

When PREEMPT_RT is enabled, the soft interrupt thread can be preempted.  If
the soft interrupt thread is preempted in the middle of a timer callback,
then calling hrtimer_cancel() can lead to two issues:

  - If the caller is on a remote CPU then it has to spin wait for the timer
    handler to complete. This can result in unbound priority inversion.

  - If the caller originates from the task which preempted the timer
    handler on the same CPU, then spin waiting for the timer handler to
    complete is never going to end.

To avoid these issues, add a new lock to the timer base which is held
around the execution of the timer callbacks. If hrtimer_cancel() detects
that the timer callback is currently running, it blocks on the expiry
lock. When the callback is finished, the expiry lock is dropped by the
softirq thread which wakes up the waiter and the system makes progress.

This addresses both the priority inversion and the life lock issues.

The same issue can happen in virtual machines when the vCPU which runs a
timer callback is scheduled out. If a second vCPU of the same guest calls
hrtimer_cancel() it will spin wait for the other vCPU to be scheduled back
in. The expiry lock mechanism would avoid that. It'd be trivial to enable
this when paravirt spinlocks are enabled in a guest, but it's not clear
whether this is an actual problem in the wild, so for now it's an RT only
mechanism.

[ tglx: Refactored it for mainline ]

Signed-off-by: Anna-Maria Gleixner 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20190726185753.737767218@linutronix.de