On 9/19/2023 11:59 AM, Jason Gunthorpe wrote:
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On Thu, Sep 14, 2023 at 04:38:37PM -0600, Alex Williamson wrote:
On Thu, 14 Sep 2023 12:15:40 -0700
Brett Creeley <brett.creeley@xxxxxxx> wrote:
The driver could possibly sleep while in atomic context resulting
in the following call trace while CONFIG_DEBUG_ATOMIC_SLEEP=y is
set:
[ 227.229806] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:283
[ 227.229818] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2817, name: bash
[ 227.229824] preempt_count: 1, expected: 0
[ 227.229827] RCU nest depth: 0, expected: 0
[ 227.229832] CPU: 5 PID: 2817 Comm: bash Tainted: G S OE 6.6.0-rc1-next-20230911 #1
[ 227.229839] Hardware name: HPE ProLiant DL360 Gen10/ProLiant DL360 Gen10, BIOS U32 01/23/2021
[ 227.229843] Call Trace:
[ 227.229848] <TASK>
[ 227.229853] dump_stack_lvl+0x36/0x50
[ 227.229865] __might_resched+0x123/0x170
[ 227.229877] mutex_lock+0x1e/0x50
[ 227.229891] pds_vfio_put_lm_file+0x1e/0xa0 [pds_vfio_pci]
[ 227.229909] pds_vfio_put_save_file+0x19/0x30 [pds_vfio_pci]
[ 227.229923] pds_vfio_state_mutex_unlock+0x2e/0x80 [pds_vfio_pci]
[ 227.229937] pci_reset_function+0x4b/0x70
[ 227.229948] reset_store+0x5b/0xa0
[ 227.229959] kernfs_fop_write_iter+0x137/0x1d0
[ 227.229972] vfs_write+0x2de/0x410
[ 227.229986] ksys_write+0x5d/0xd0
[ 227.229996] do_syscall_64+0x3b/0x90
[ 227.230004] entry_SYSCALL_64_after_hwframe+0x6e/0xd8
[ 227.230017] RIP: 0033:0x7fb202b1fa28
[ 227.230023] Code: 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 8d 05 15 4d 2a 00 8b 00 85 c0 75 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 49 89 d4 55
[ 227.230028] RSP: 002b:00007fff6915fbd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 227.230036] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007fb202b1fa28
[ 227.230040] RDX: 0000000000000002 RSI: 000055f3834d5aa0 RDI: 0000000000000001
[ 227.230044] RBP: 000055f3834d5aa0 R08: 000000000000000a R09: 00007fb202b7fae0
[ 227.230047] R10: 000000000000000a R11: 0000000000000246 R12: 00007fb202dc06e0
[ 227.230050] R13: 0000000000000002 R14: 00007fb202dbb860 R15: 0000000000000002
[ 227.230056] </TASK>
I usually encourage people to trim the oops, remove the time stamp at least.
Makes sense. I will remember that going forward. Thanks for the suggestion.
Brett
This can happen if pds_vfio_put_restore_file() and/or
pds_vfio_put_save_file() grab the mutex_lock(&lm_file->lock)
while the spin_lock(&pds_vfio->reset_lock) is held, which can
happen during while calling pds_vfio_state_mutex_unlock().
Fix this by releasing the spin_unlock(&pds_vfio->reset_lock) before
calling pds_vfio_put_restore_file() and pds_vfio_put_save_file() and
re-acquiring spin_lock(&pds_vfio->reset_lock) after the previously
mentioned functions are called to protect setting the subsequent
state/deferred reset settings.
The only possible concerns are other threads that may call
pds_vfio_put_restore_file() and/or pds_vfio_put_save_file(). However,
those paths are already protected by the state mutex_lock().
Is there another viable solution to change reset_lock to a mutex?
I think this is the origin of this algorithm:
https://lore.kernel.org/all/20211019191025.GA4072278@xxxxxxxxxx/
But it's not clear to me why Jason chose an example with a spinlock and
if some subtlety here requires it. Thanks,
I think there was no specific reason it must be a spinlock
Certainly I'm not feeling comfortable just unlocking and relocking
like that. It would need a big explanation why it is safe in a
comment.
This follows the example in mlx5vf_state_mutex_unlock(), which releases
the spinlock before calling mlx5vf_disable_fds().
However, there is a small difference where
pds_vfio->deferred_reset_state could change in the window where the
reset_lock isn't held. It seems this can be fixed this by a local
deferred_reset_state in pds_vfio_state_mutex_unlock() that I set before
unlocking to clear the fds.
Thanks,
Brett
Jason
