Re: [patch V3 06/18] posix-timers: Remove SLAB_PANIC from kmem cache

Re: [patch V3 06/18] posix-timers: Remove SLAB_PANIC from kmem cache

[Alexey Dobriyan]

> -	posix_timers_cache = kmem_cache_create("posix_timers_cache",
> -					sizeof(struct k_itimer), 0,
> -					SLAB_PANIC | SLAB_ACCOUNT, NULL);
> +	posix_timers_cache = kmem_cache_create("posix_timers_cache", sizeof(struct k_itimer), 0,
> +					       SLAB_ACCOUNT, NULL);

> There is no need to panic when the posix-timer kmem_cache can't be
> created. timer_create() will fail with -ENOMEM and that's it.

Of course there is a reason to panic.

Where did the  memory go, so there is not enough for a tiny
"kmem_cache" instance?

You've taken the branch from __init code which is discarded
and made it a branch which can not be.

More or less every __init allocation should panic not the other way
around.

[patch V3 00/18] posix-timers: Rework the global hash table and provide a sane mechanism for CRIU

[Thomas Gleixner]

This is a follow up on V2 of this work, which can be found here:

     https://lore.kernel.org/all/20250224095736.145530367@linutronix.de

It addresses the scalability problem of the posix timer hash and provides a
performant mechanism to restore Posix timers with a given ID along with a
couple of preperatory cleanups and enhancements. More details about
implementation choices are in the change logs and the cover letter of V1:

     https://lore.kernel.org/all/20250302185753.311903554@linutronix.de

Changes vs. V2:

  - Ensure consistency on timer_create() (new patch) - Frederic
  - Pick up the lock_timer() conditional unlock fix (was V2a)
  - Use proper defines in selftests
  - Pick up review/ack tags

The series survives all posix timer tests and did not show any regressions
so far.

The series is based on:

    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip timers/core

and is also available from git:

    git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git timers/posix

Thanks,

	tglx
---
Eric Dumazet (3):
      posix-timers: Initialise timer before adding it to the hash table
      posix-timers: Add cond_resched() to posix_timer_add() search loop
      posix-timers: Make signal_struct:: Next_posix_timer_id an atomic_t

Peter Zijlstra (1):
      posix-timers: Make lock_timer() use guard()

Thomas Gleixner (14):
      posix-timers: Ensure that timer initialization is fully visible
      posix-timers: Cleanup includes
      posix-timers: Remove a few paranoid warnings
      posix-timers: Remove SLAB_PANIC from kmem cache
      posix-timers: Use guards in a few places
      posix-timers: Simplify lock/unlock_timer()
      posix-timers: Rework timer removal
      posix-timers: Improve hash table performance
      posix-timers: Switch to jhash32()
      posix-timers: Avoid false cacheline sharing
      posix-timers: Make per process list RCU safe
      posix-timers: Dont iterate /proc/$PID/timers with sighand:: Siglock held
      posix-timers: Provide a mechanism to allocate a given timer ID
      selftests/timers/posix-timers: Add a test for exact allocation mode


 fs/proc/base.c                                |   48 --
 include/linux/cleanup.h                       |   22 -
 include/linux/posix-timers.h                  |   30 +
 include/linux/sched/signal.h                  |    3 
 include/uapi/linux/prctl.h                    |   10 
 kernel/signal.c                               |    2 
 kernel/sys.c                                  |    5 
 kernel/time/posix-timers.c                    |  540 +++++++++++++-------------
 tools/testing/selftests/timers/posix_timers.c |   66 +++
 9 files changed, 418 insertions(+), 308 deletions(-)

[patch V3 06/18] posix-timers: Remove SLAB_PANIC from kmem cache

[Thomas Gleixner]

There is no need to panic when the posix-timer kmem_cache can't be
created. timer_create() will fail with -ENOMEM and that's it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
---
V2: New patch
---
 kernel/time/posix-timers.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -243,9 +243,8 @@ static int posix_get_hrtimer_res(clockid
 
 static __init int init_posix_timers(void)
 {
-	posix_timers_cache = kmem_cache_create("posix_timers_cache",
-					sizeof(struct k_itimer), 0,
-					SLAB_PANIC | SLAB_ACCOUNT, NULL);
+	posix_timers_cache = kmem_cache_create("posix_timers_cache", sizeof(struct k_itimer), 0,
+					       SLAB_ACCOUNT, NULL);
 	return 0;
 }
 __initcall(init_posix_timers);
@@ -371,8 +370,12 @@ static struct pid *good_sigevent(sigeven
 
 static struct k_itimer *alloc_posix_timer(void)
 {
-	struct k_itimer *tmr = kmem_cache_zalloc(posix_timers_cache, GFP_KERNEL);
+	struct k_itimer *tmr;
 
+	if (unlikely(!posix_timers_cache))
+		return NULL;
+
+	tmr = kmem_cache_zalloc(posix_timers_cache, GFP_KERNEL);
 	if (!tmr)
 		return tmr;