| Message ID | 20211222114111.2206248-1-bigeasy@linutronix.de (mailing list archive) |
|---|---|
| Headers | show |
| Series | mm/memcg: Address PREEMPT_RT problems instead of disabling it. | expand |
On Wed, Dec 22, 2021 at 12:41:08PM +0100, Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote: > - lockdep complains were triggered by test_core and test_freezer (both > had to run): This doesn't happen on the patched kernel, correct? Thanks, Michal
On 2022-01-05 15:59:56 [+0100], Michal Koutný wrote: > On Wed, Dec 22, 2021 at 12:41:08PM +0100, Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote: > > - lockdep complains were triggered by test_core and test_freezer (both > > had to run): > > This doesn't happen on the patched kernel, correct? I saw it first on the patched kernel (with this series) then went back to the -rc and saw it there, too. > Thanks, > Michal Sebastian
Hi, this is a follow up to https://lkml.kernel.org/r/20211207155208.eyre5svucpg7krxe@linutronix.de where it has been suggested that I should try again with memcg instead of simply disabling it. Patch #1 deals with the counters. It has been suggested to simply disable preemption on RT (like in vmstats) and I followed that advice as closely as possible. The local_irq_save() could be removed from mod_memcg_state() and the other wrapper on RT but I leave it since it does not hurt and it might look nicer ;) Patch #2 is a follow up to https://lkml.kernel.org/r/20211214144412.447035-1-longman@redhat.com Patch #3 restricts the task_obj usage to !PREEMPTION kernels. Based on my understanding the use of preempt_disable() minimizes (avoids?) the win of the optimisation. I tested them on CONFIG_PREEMPT_NONE + CONFIG_PREEMPT_RT with the tools/testing/selftests/cgroup/* tests. I looked good except for the following (which was also there before the patches): - test_kmem sometimes complained about: not ok 2 test_kmem_memcg_deletion - test_memcontrol complained always about not ok 3 test_memcg_min not ok 4 test_memcg_low and did not finish. - lockdep complains were triggered by test_core and test_freezer (both had to run): ====================================================== WARNING: possible circular locking dependency detected 5.16.0-rc5 #259 Not tainted ------------------------------------------------------ test_core/5996 is trying to acquire lock: ffffffff829a1258 (css_set_lock){..-.}-{2:2}, at: obj_cgroup_release+0x2d/0xb0 but task is already holding lock: ffff888103034618 (&sighand->siglock){....}-{2:2}, at: get_signal+0x8d/0xdb0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&sighand->siglock){....}-{2:2}: _raw_spin_lock+0x27/0x40 cgroup_post_fork+0x1f5/0x290 copy_process+0x191b/0x1f80 kernel_clone+0x5a/0x410 __do_sys_clone3+0xb3/0x110 do_syscall_64+0x43/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #0 (css_set_lock){..-.}-{2:2}: __lock_acquire+0x1253/0x2280 lock_acquire+0xd4/0x2e0 _raw_spin_lock_irqsave+0x36/0x50 obj_cgroup_release+0x2d/0xb0 drain_obj_stock+0x1a9/0x1b0 refill_obj_stock+0x4f/0x220 memcg_slab_free_hook.part.0+0x108/0x290 kmem_cache_free+0xf5/0x3c0 dequeue_signal+0xaf/0x1e0 get_signal+0x232/0xdb0 arch_do_signal_or_restart+0xf8/0x740 exit_to_user_mode_prepare+0x17d/0x270 syscall_exit_to_user_mode+0x19/0x70 do_syscall_64+0x50/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&sighand->siglock); lock(css_set_lock); lock(&sighand->siglock); lock(css_set_lock); *** DEADLOCK *** 2 locks held by test_core/5996: #0: ffff888103034618 (&sighand->siglock){....}-{2:2}, at: get_signal+0x8d/0xdb0 #1: ffffffff82905e40 (rcu_read_lock){....}-{1:2}, at: drain_obj_stock+0x71/0x1b0 stack backtrace: CPU: 2 PID: 5996 Comm: test_core Not tainted 5.16.0-rc5 #259 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x45/0x59 check_noncircular+0xfe/0x110 __lock_acquire+0x1253/0x2280 lock_acquire+0xd4/0x2e0 _raw_spin_lock_irqsave+0x36/0x50 obj_cgroup_release+0x2d/0xb0 drain_obj_stock+0x1a9/0x1b0 refill_obj_stock+0x4f/0x220 memcg_slab_free_hook.part.0+0x108/0x290 kmem_cache_free+0xf5/0x3c0 dequeue_signal+0xaf/0x1e0 get_signal+0x232/0xdb0 arch_do_signal_or_restart+0xf8/0x740 exit_to_user_mode_prepare+0x17d/0x270 syscall_exit_to_user_mode+0x19/0x70 do_syscall_64+0x50/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae </TASK> Sebastian