[Bug 274271] zfs deadlock while/after writing files

From: <bugzilla-noreply_at_freebsd.org>
Date: Wed, 04 Oct 2023 23:27:35 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=274271

            Bug ID: 274271
           Summary: zfs deadlock while/after writing files
           Product: Base System
           Version: 13.2-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: pmc@citylink.dinoex.sub.org

After building ports for 47+ hours, finally the clone of /usr/ports should be
exported; but then zfs was tired and deadlocked:

 UID   PID  PPID  C PRI NI      VSZ      RSS MWCHAN   STAT TT          TIME
COMM
   0 40329 41971 13 134  0   302596   151632 select   IN+   3       0:05.97 git
-C /var/sysup/mnt/tmp.6.41971 checkout-index -a
--prefix=/var/sysup/mnt/tmp.8.41971/
   0 40678 40329 14 134  0        0        0 -        ZN+   3       0:02.08
<defunct>
   0 40679 40329 10 134  0        0        0 -        ZN+   3       0:02.06
<defunct>
   0 40680 40329  0 134  0        0        0 -        ZN+   3       0:02.08
<defunct>
   0 40681 40329  8 134  0   682132   165796 zfsvfs-> DN+   3       0:00.99
/usr/local/libexec/git-core/git checkout--worker
--prefix=/var/sysup/mnt/tmp.8.41971/
   0 40682 40329 11 134  0        0        0 -        ZN+   3       0:02.35
<defunct>
   0 40683 40329  0 134  0        0        0 -        ZN+   3       0:02.37
<defunct>
   0 40684 40329  8 134  0        0        0 -        ZN+   3       0:03.11
<defunct>

killing of the git process is not possible, umount of the fs is not possible,
reboot will also fail (get stuck).

scrub of the concerned pool is still possible and shows no errors. Neither are
any errors reported from the disks or the ECC memory.

  pool: build
 state: ONLINE
  scan: scrub repaired 0B in 00:15:11 with 0 errors on Wed Oct  4 23:34:26 2023
config:

        NAME               STATE     READ WRITE CKSUM
        build              ONLINE       0     0     0
          raidz1-0         ONLINE       0     0     0
            da3p1.eli      ONLINE       0     0     0
            da4p1.eli      ONLINE       0     0     0
            da5p1.eli      ONLINE       0     0     0
        special
          mirror-1         ONLINE       0     0     0
            ada1p9.elip10  ONLINE       0     0     0
            ada6p9.elip10  ONLINE       0     0     0
        cache
          ada3p9.elip6     ONLINE       0     0     0

errors: No known data errors

The last command in zpool history before the deadlock is
2023-10-04.22:30:58 zfs create -o mountpoint=legacy build/tmp.7.41971

This was then legacy-mounted to /var/sysup/mnt/tmp.8.41971/ and the git process
started, which didn't complete.

The fileset has received most/all of the data (the other git workers have 
apparently completed):
build/tmp.7.41971                                  970M  63.0G      970M 
legacy

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