Messages in this thread | | | Date | Fri, 17 Jun 2022 10:29:20 -0400 | Subject | Re: Lockups due to "locking/rwsem: Make handoff bit handling more consistent" | From | Waiman Long <> |
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On 6/17/22 09:43, Mel Gorman wrote: > Hi Waiman, > > I've received reports of lockups happening in kernels including > commit d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more > consistent"). The exact symptoms vary but usually it's either a soft lockup > (older kernel with a backport), the task hanging and never exiting or the > machine becomes generally unresponsive and ssh is broken. The problem > started in 5.16 and reliably bisected to commit d257cc8cb8d5. Reverting > the patch in 5.16, 5.17 and 5.18 finish the test successfully but I didn't > test a revert on 5.19-rc2 because of other changes layered on top. > > The reproducer is simple -- start pairs of CPU hogs pinned to a CPU with > different SCHED_RR priorities that run for a few seconds. It does not > hit every time but usually happens within 10 attempts. On 5.16 at least, > the tasks failed to exit and kept retrying to exit using the following path > > [<0>] rwsem_down_write_slowpath+0x2ad/0x580 > [<0>] unlink_file_vma+0x2c/0x50 > [<0>] free_pgtables+0xbe/0x110 > [<0>] exit_mmap+0xc1/0x220 > [<0>] mmput+0x52/0x110 > [<0>] do_exit+0x2ec/0xb00 > [<0>] do_group_exit+0x2d/0x90 > [<0>] get_signal+0xb6/0x920 > [<0>] arch_do_signal_or_restart+0xba/0x700 > [<0>] exit_to_user_mode_prepare+0xb7/0x230 > [<0>] irqentry_exit_to_user_mode+0x5/0x20 > [<0>] asm_sysvec_apic_timer_interrupt+0x12/0x20 > [<0>] preempt_schedule_thunk+0x16/0x18 > [<0>] rwsem_down_write_slowpath+0x2ad/0x580 > [<0>] unlink_file_vma+0x2c/0x50 > [<0>] free_pgtables+0xbe/0x110 > [<0>] exit_mmap+0xc1/0x220 > [<0>] mmput+0x52/0x110 > [<0>] do_exit+0x2ec/0xb00 > [<0>] do_group_exit+0x2d/0x90 > [<0>] get_signal+0xb6/0x920 > [<0>] arch_do_signal_or_restart+0xba/0x700 > [<0>] exit_to_user_mode_prepare+0xb7/0x230 > [<0>] irqentry_exit_to_user_mode+0x5/0x20 > [<0>] asm_sysvec_apic_timer_interrupt+0x12/0x20 > > The C file and shell script to run it are attached. > Thanks for the reproducer and I will try to reproduce it locally.
It is a known issue that I have receive similar report from an Oracle engineer. That is the reason I posted commit 1ee326196c66 ("locking/rwsem: Always try to wake waiters in out_nolock path") that was merged in v5.19. I believe it helps but it may not be able to eliminate all possible race conditions. To make rwsem behave more like before commit d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more consistent"), I posted a follow-up patch
https://lore.kernel.org/lkml/20220427173124.1428050-1-longman@redhat.com/
But it hasn't gotten review yet.
I will try your reproducer to see if these patches are able to address the lockup problem.
Thanks, Longman
commit d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more consistent").
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