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

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Message-ID: <8fdf4fe3-dd68-4b60-87f3-2607aaa2279c@kadam.mountain>
Date:   Wed, 13 Sep 2023 20:51:14 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     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 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.

regards,
dan carpenter