RHEL8 : panic while breaking a lease/delegation after user mode helper invocation

Solution In Progress - Updated -

Issue

Host panics with the following stack :


[ 83.642293] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010 [ 83.642329] PGD 0 P4D 0 [ 83.642338] Oops: 0000 [#1] SMP NOPTI [ 83.642348] CPU: 1 PID: 5425 Comm: kworker/u8:2 Kdump: loaded Not tainted 4.18.0-305.3.1.el8_4.x86_64 #1 [ 83.642367] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2.fc34 04/01/2014 [ 83.642391] RIP: 0010:kthread_func+0x15/0x20 [ 83.642401] Code: 68 10 01 75 b7 48 8b 40 20 e8 07 c1 af 00 eb ac 0f 1f 44 00 00 0f 1f 44 00 00 31 c0 f6 47 26 20 75 01 c3 48 8b 87 d8 09 00 00 <48> 8b 40 10 c3 66 0f 1f 44 00 00 0f 1f 44 00 00 65 48 8b 14 25 40 [ 83.642441] RSP: 0018:ffffb360c12f3b38 EFLAGS: 00010202 [ 83.642457] RAX: 0000000000000000 RBX: ffff96c38ff4e738 RCX: ffff96c38d715b88 [ 83.642472] RDX: ffff96c38d7120e0 RSI: ffff96c38d7126c0 RDI: ffff96c396528000 [ 83.642492] RBP: ffff96c38d7120d8 R08: ffffb360c12f3b38 R09: ffff96c38d7126c0 [ 83.642507] R10: ffffb360c12f3c38 R11: 0000000000000000 R12: ffff96c38d7126c0 [ 83.642522] R13: ffffffffb5f05d80 R14: 000000008d7126c0 R15: ffff96c3b636c000 [ 83.642537] FS: 0000000000000000(0000) GS:ffff96c3bbc80000(0000) knlGS:0000000000000000 [ 83.642557] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 83.642570] CR2: 0000000000000010 CR3: 0000000009810004 CR4: 0000000000770ee0 [ 83.642587] PKRU: 55555554 [ 83.642594] Call Trace: [ 83.642652] i_am_nfsd+0x13/0x20 [nfsd] [ 83.642680] nfsd_breaker_owns_lease+0xf/0x40 [nfsd] [ 83.642700] leases_conflict+0x28/0xd0 [ 83.642725] any_leases_conflict.isra.30+0x37/0x50 [ 83.642742] __break_lease+0xc2/0x510 [ 83.642753] do_dentry_open+0x10d/0x340 [ 83.642768] path_openat+0x53e/0x14f0 [ 83.642783] do_filp_open+0x93/0x100 [ 83.642801] ? kmemdup+0x2d/0x40 [ 83.642810] do_open_execat+0x83/0x1a0 [ 83.642821] do_execveat_common.isra.37+0x1d0/0x8b0 [ 83.642833] ? getname_kernel+0x2c/0x100 [ 83.642842] do_execve+0x1f/0x30 [ 83.642852] call_usermodehelper_exec_async+0xf0/0x150 [ 83.642873] ? recalc_sigpending+0x17/0x50 [ 83.642885] ? call_usermodehelper+0xa0/0xa0 [ 83.642897] ret_from_fork+0x1f/0x40

Environment

  • RHEL8.4, NFS server
  • Delegations enabled (its default)
  • /usr filesystem exported

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