Re: [PATCH v5] locking/rwsem: Make handoff bit handling more consistent

[john . p . donnelly]

On 4/26/22 3:21 PM, Waiman Long wrote:
> On 4/20/22 09:55, john.p.donnelly@xxxxxxxxxx wrote:
> > On 4/12/22 11:28 AM, john.p.donnelly@xxxxxxxxxx wrote:
> > > On 4/11/22 4:07 PM, Waiman Long wrote:
> > > > On 4/11/22 17:03, john.p.donnelly@xxxxxxxxxx wrote:
> > > > > > > I have reached out to Waiman and he suggested this for our next 
> > > > > > > test pass:
> > > > > > >
> > > > > > >
> > > > > > > 1ee326196c6658 locking/rwsem: Always try to wake waiters in 
> > > > > > > out_nolock path
> > > > > >
> > > > > > Does this commit help to avoid the lockup problem?
> > > > > >
> > > > > > Commit 1ee326196c6658 fixes a potential missed wakeup problem when 
> > > > > > a reader first in the wait queue is interrupted out without 
> > > > > > acquiring the lock. It is actually not a fix for commit 
> > > > > > d257cc8cb8d5. However, this commit changes the out_nolock path 
> > > > > > behavior of writers by leaving the handoff bit set when the wait 
> > > > > > queue isn't empty. That likely makes the missed wakeup problem 
> > > > > > easier to reproduce.
> > > > > >
> > > > > > Cheers,
> > > > > > Longman
> > > > >
> > > > > Hi,
> > > > >
> > > > >
> > > > > We are testing now
> > > > >
> > > > > ETA for fio soak test completion is  ~15hr from now.
> > > > >
> > > > > I wanted to share the stack traces for future reference + occurrences.
> > > > I am looking forward to your testing results tomorrow.
> > > >
> > > > Cheers,
> > > > Longman
> > > Hi
> > >
> > >   Our 24hr fio soak test with :
> > >
> > >   1ee326196c6658 locking/rwsem: Always try to wake waiters in 
> > > out_nolock path
> > >
> > >
> > >   applied to 5.15.30  passed.
> > >
> > >   I suggest you append  1ee326196c6658 with :
> > >
> > >
> > >   cc: stable
> > >
> > >    Fixes: d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling 
> > > more consistent")
> > >
> > >
> > > I'll leave the implementation details up to the core maintainers how 
> > > to do that ;-)
> > >
> > > ...
> > >
> > > Thank you
> > >
> > > John.
> >
> > Hi ,
> >
> >
> >  We have observed another panic with :
> >
> >  1ee326196c6658 locking/rwsem: Always try to wake waiters in out_nolock
> >  path
> >
> >  Applied to 5.15.30 :
> Sorry for the late reply as I was busy with other important tasks.
>
> When you said panic, you mean a system hang, not an actual panic. Right?

Hi ,

Our setups turn on all the panic on-hung-task , on-opps,  all those 
various features:

./sys/kernel/hardlockup_panic
./sys/kernel/hung_task_panic
./sys/kernel/max_rcu_stall_to_panic
./sys/kernel/panic
./sys/kernel/panic_on_io_nmi
./sys/kernel/panic_on_oops
./sys/kernel/panic_on_rcu_stall
./sys/kernel/panic_on_unrecovered_nmi
./sys/kernel/panic_on_warn
./sys/kernel/panic_print
./sys/kernel/softlockup_panic
./sys/kernel/unknown_nmi_panic


The machine is unusable when this occurs.


> > PID: 3789   TASK: ffff900fc409b300  CPU: 29  COMMAND: "dio/dm-0"
> >  #0 [fffffe00006bce50] crash_nmi_callback at ffffffff97c772c3
> >  #1 [fffffe00006bce58] nmi_handle at ffffffff97c40778
> >  #2 [fffffe00006bcea0] default_do_nmi at ffffffff988161e2
> >  #3 [fffffe00006bcec8] exc_nmi at ffffffff9881648d
> >  #4 [fffffe00006bcef0] end_repeat_nmi at ffffffff98a0153b
> >     [exception RIP: _raw_spin_lock_irq+35]
> >     RIP: ffffffff98827333  RSP: ffffa9320917fc78  RFLAGS: 00000046
> >     RAX: 0000000000000000  RBX: ffff900fc409b300  RCX: 0000000000000000
> >     RDX: 0000000000000000  RSI: 0000000000000000  RDI: 0000000000000000
> >     RBP: ffffa9320917fd20   R8: 0000000000000000   R9: 0000000000000000
> >     R10: 0000000000000000  R11: 0000000000000000  R12: ffff90006259546c
> >     R13: ffffa9320917fcb0  R14: ffff900062595458  R15: 0000000000000000
> >     ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
> > --- <NMI exception stack> ---
> >  #5 [ffffa9320917fc78] _raw_spin_lock_irq at ffffffff98827333
> >  #6 [ffffa9320917fc78] rwsem_down_write_slowpath at ffffffff97d25d49
> >  #7 [ffffa9320917fd28] ext4_map_blocks at ffffffffc104b6dc [ext4]
> >  #8 [ffffa9320917fd98] ext4_convert_unwritten_extents at 
> > ffffffffc10369e0 [ext4]
> >  #9 [ffffa9320917fdf0] ext4_dio_write_end_io at ffffffffc103b2aa [ext4]
> > #10 [ffffa9320917fe18] iomap_dio_complete at ffffffff98013f45
> > #11 [ffffa9320917fe48] iomap_dio_complete_work at ffffffff98014047
> > #12 [ffffa9320917fe60] process_one_work at ffffffff97cd9191
> > #13 [ffffa9320917fea8] rescuer_thread at ffffffff97cd991b
> > #14 [ffffa9320917ff10] kthread at ffffffff97ce11f7
> > #15 [ffffa9320917ff50] ret_from_fork at ffffffff97c04cf2
> > crash>
> >
> >
> > The failure is observed running "fio test suite"  as a 24 hour soak 
> > test  on an LVM composed of four NVME devices, Intel 72 core server. 
> > The test cycles through a variety of file-system types.
> >
> >
> > This kernel has these commits
> >
> > 1ee326196c6658 locking/rwsem: Always try to wake waiters in 
> > out_nolock  path
> >
> > d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more consistent")
> >
> > In earlier testing I had reverted d257cc8cb8d5 and did not observe 
> > said panics.  I still feel d257cc8cb8d5 is  still the root cause.
>
> So it is possible that 1ee326196c6658 does not completely eliminate the 
> missed wakeup situation.
>
> Regards,
> Longman