linux-kernel - Re: [PATCH vfio] pds/vfio: Fix possible sleep while in atomic context

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Message-ID: <8749a8f6-d756-dabe-63b1-344221873d99@amd.com>
Date:   Wed, 13 Sep 2023 10:57:28 -0700
From:   Brett Creeley <bcreeley@....com>
To:     Dan Carpenter <dan.carpenter@...aro.org>,
        Brett Creeley <brett.creeley@....com>
Cc:     jgg@...pe.ca, yishaih@...dia.com,
        shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
        alex.williamson@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, shannon.nelson@....com
Subject: Re: [PATCH vfio] pds/vfio: Fix possible sleep while in atomic context

On 9/13/2023 10:51 AM, Dan Carpenter wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
> 
> 
> On Wed, Sep 13, 2023 at 10:42:38AM -0700, Brett Creeley wrote:
>> 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 splat doesn't match the sleeping in atomic bug at all.  That
> warning should have said, "BUG: sleeping function called from invalid
> context" and the stack trace would have looked totally different.
> 
> I don't have a problem with the patch itself, that seems reasonable.  I
> really like that you tested it but you're running into a different
> bug here.  Hopefully, you just pasted the wrong splat but otherwise we
> need to investigate this other "bad magic" bug.

Hmm, good catch. Let me double check this and get back to you.

Thanks for the quick response and review.

Brett

> 
> regards,
> dan carpenter
>