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From:   Brett Creeley <brett.creeley@amd.com>
To:     <jgg@ziepe.ca>, <yishaih@nvidia.com>,
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        <brett.creeley@amd.com>, <shannon.nelson@amd.com>
Subject: [PATCH vfio] pds/vfio: Fix possible sleep while in atomic context
Date:   Wed, 13 Sep 2023 10:42:38 -0700
Message-ID: <20230913174238.72205-1-brett.creeley@amd.com>
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The driver could possibly sleep while in atomic context resulting
in the following call trace while CONFIG_DEBUG_ATOMIC_SLEEP=y is
set:

[  675.116953] BUG: spinlock bad magic on CPU#2, bash/2481
[  675.116966]  lock: 0xffff8d6052a88f50, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
[  675.116978] CPU: 2 PID: 2481 Comm: bash Tainted: G S                 6.6.0-rc1-next-20230911 #1
[  675.116986] Hardware name: HPE ProLiant DL360 Gen10/ProLiant DL360 Gen10, BIOS U32 01/23/2021
[  675.116991] Call Trace:
[  675.116997]  <TASK>
[  675.117002]  dump_stack_lvl+0x36/0x50
[  675.117014]  do_raw_spin_lock+0x79/0xc0
[  675.117032]  pds_vfio_reset+0x1d/0x60 [pds_vfio_pci]
[  675.117049]  pci_reset_function+0x4b/0x70
[  675.117061]  reset_store+0x5b/0xa0
[  675.117074]  kernfs_fop_write_iter+0x137/0x1d0
[  675.117087]  vfs_write+0x2de/0x410
[  675.117101]  ksys_write+0x5d/0xd0
[  675.117111]  do_syscall_64+0x3b/0x90
[  675.117122]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
[  675.117135] RIP: 0033:0x7f9ebbd1fa28
[  675.117141] 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
[  675.117148] RSP: 002b:00007ffdff410728 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[  675.117156] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007f9ebbd1fa28
[  675.117161] RDX: 0000000000000002 RSI: 000055ffc5fdf7c0 RDI: 0000000000000001
[  675.117166] RBP: 000055ffc5fdf7c0 R08: 000000000000000a R09: 00007f9ebbd7fae0
[  675.117170] R10: 000000000000000a R11: 0000000000000246 R12: 00007f9ebbfc06e0
[  675.117174] R13: 0000000000000002 R14: 00007f9ebbfbb860 R15: 0000000000000002
[  675.117180]  </TASK>


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().

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/kvm/1f9bc27b-3de9-4891-9687-ba2820c1b390@moroto.mountain/
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
Signed-off-by: Brett Creeley <brett.creeley@amd.com>
---
 drivers/vfio/pci/pds/vfio_dev.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/vfio/pci/pds/vfio_dev.c b/drivers/vfio/pci/pds/vfio_dev.c
index b46174f5eb09..0807d163f83e 100644
--- a/drivers/vfio/pci/pds/vfio_dev.c
+++ b/drivers/vfio/pci/pds/vfio_dev.c
@@ -33,8 +33,10 @@ void pds_vfio_state_mutex_unlock(struct pds_vfio_pci_device *pds_vfio)
 	if (pds_vfio->deferred_reset) {
 		pds_vfio->deferred_reset = false;
 		if (pds_vfio->state == VFIO_DEVICE_STATE_ERROR) {
+			spin_unlock(&pds_vfio->reset_lock);
 			pds_vfio_put_restore_file(pds_vfio);
 			pds_vfio_put_save_file(pds_vfio);
+			spin_lock(&pds_vfio->reset_lock);
 			pds_vfio_dirty_disable(pds_vfio, false);
 		}
 		pds_vfio->state = pds_vfio->deferred_reset_state;
-- 
2.17.1