Re: pktcdvd ->open_mutex lockdep splat

[Brian Foster <bfoster@redhat.com>]

On Fri, Mar 22, 2024 at 12:40:21PM -0400, Brian Foster wrote:
> Hi all,
> 
> I noticed the splat below on one of my test VMs when running latest
> upstream with lockdep enabled. I'm not really sure why this occurs
> because I'm not actually using this device for anything I'm aware of. I
> suppose it's possible this has a busted userspace or kvm config, as this
> is just one of a handful of scratch VMs I have around for development
> purposes. I'm happy to try and dig further into it or just expunge it if
> this is of little interest.
> 

Ok, I guess the reason I was only seeing this in one particular VM is
that for whatever reason, something happens to invoke pktsetup during
boot on that guest. If I boot up a separate VM/distro and run 'pktsetup
0 /dev/sr0,' I see the same splat..

Brian

> FWIW, the splat itself reproduces back before ->open_mutex was created
> from bd_mutex by commit a8698707a183 ("block: move bd_mutex to struct
> gendisk"). I went as far back as v5.10 and still observed it.
> 
> Brian
> 
> --- 8< ---
> 
> [   11.667694] block (null): writer mapped to sr0
> 
> [   11.677407] ============================================
> [   11.680650] WARNING: possible recursive locking detected
> [   11.683581] 6.8.0+ #346 Tainted: G            E     
> [   11.686246] --------------------------------------------
> [   11.689075] systemd-udevd/1438 is trying to acquire lock:
> [   11.690607] ffff8bb78f553cc8 (&disk->open_mutex){+.+.}-{3:3}, at: bdev_open+0x60/0x3e0
> [   11.692504] 
>                but task is already holding lock:
> [   11.693921] ffff8bb786b39cc8 (&disk->open_mutex){+.+.}-{3:3}, at: bdev_open+0x239/0x3e0
> [   11.695806] 
>                other info that might help us debug this:
> [   11.697362]  Possible unsafe locking scenario:
> 
> [   11.698779]        CPU0
> [   11.699397]        ----
> [   11.699994]   lock(&disk->open_mutex);
> [   11.700923]   lock(&disk->open_mutex);
> [   11.701849] 
>                 *** DEADLOCK ***
> 
> [   11.703273]  May be due to missing lock nesting notation
> 
> [   11.704878] 3 locks held by systemd-udevd/1438:
> [   11.705967]  #0: ffff8bb786b39cc8 (&disk->open_mutex){+.+.}-{3:3}, at: bdev_open+0x239/0x3e0
> [   11.707966]  #1: ffffffffc085c768 (pktcdvd_mutex){+.+.}-{3:3}, at: pkt_open+0x2b/0x630 [pktcdvd]
> [   11.710080]  #2: ffffffffc085d868 (&ctl_mutex#2){+.+.}-{3:3}, at: pkt_open+0x39/0x630 [pktcdvd]
> [   11.712164] 
>                stack backtrace:
> [   11.713200] CPU: 3 PID: 1438 Comm: systemd-udevd Tainted: G            E      6.8.0+ #346
> [   11.715122] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014
> [   11.717123] Call Trace:
> [   11.717741]  <TASK>
> [   11.718271]  dump_stack_lvl+0x79/0xb0
> [   11.719194]  __lock_acquire+0x1228/0x2170
> [   11.720172]  lock_acquire+0xbb/0x2c0
> [   11.721030]  ? bdev_open+0x60/0x3e0
> [   11.721869]  __mutex_lock+0x77/0xd40
> [   11.722724]  ? bdev_open+0x60/0x3e0
> [   11.723558]  ? find_held_lock+0x2b/0x80
> [   11.724470]  ? bdev_open+0x56/0x3e0
> [   11.725324]  ? bdev_open+0x60/0x3e0
> [   11.726173]  ? bdev_open+0x60/0x3e0
> [   11.727031]  bdev_open+0x60/0x3e0
> [   11.727844]  bdev_file_open_by_dev+0xbf/0x120
> [   11.728909]  pkt_open+0x10e/0x630 [pktcdvd]
> [   11.729944]  ? bdev_open+0x22f/0x3e0
> [   11.730815]  ? lock_release+0xb8/0x270
> [   11.731729]  ? bdev_open+0x239/0x3e0
> [   11.732605]  blkdev_get_whole+0x25/0x90
> [   11.733544]  bdev_open+0x29f/0x3e0
> [   11.734380]  ? iput.part.0+0x34/0x260
> [   11.735277]  ? __pfx_blkdev_open+0x10/0x10
> [   11.736282]  blkdev_open+0x8b/0xc0
> [   11.737090]  do_dentry_open+0x172/0x580
> [   11.738002]  path_openat+0x3a9/0xa30
> [   11.738864]  do_filp_open+0xa1/0x130
> [   11.739731]  ? _raw_spin_unlock+0x23/0x40
> [   11.740700]  do_sys_openat2+0x82/0xb0
> [   11.741596]  __x64_sys_openat+0x49/0x80
> [   11.742529]  do_syscall_64+0x7c/0x190
> [   11.743406]  entry_SYSCALL_64_after_hwframe+0x6c/0x74
> [   11.744599] RIP: 0033:0x7f30e4afd70b
> [   11.745450] Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00 00 00 85 c0 75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 91 00 00 00 48 8b 54 24 28 64 48 2b 14 25
> [   11.749817] RSP: 002b:00007ffdafd13250 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
> [   11.751633] RAX: ffffffffffffffda RBX: 0000000000006000 RCX: 00007f30e4afd70b
> [   11.753306] RDX: 0000000000080900 RSI: 00007ffdafd132d0 RDI: 00000000ffffff9c
> [   11.754966] RBP: 00007ffdafd132d0 R08: 0000000000000000 R09: 00007ffdafd13160
> [   11.756624] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000080900
> [   11.758311] R13: 0000000000080900 R14: 0000000000000006 R15: 00007ffdafd13470
> [   11.760041]  </TASK>
> 
>