mounting cifs share causes Oops - kernel NULL pointer dereference

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Environment

SUSE Linux Enterprise Server 15 SP6

Situation

After updating SP6 to kernel: 6.4.0-150600.23.7.3 or 6.4.0-150600.23.14.2 and mounting CIFS shares, the system hangs.

Relevant parts of the traces could look like this:

[ xxxxxx] CIFS: Attempting to mount //<IP>/cifs/share/
[ xxxxxx ] CPU: 1 PID: 2859 Comm: ls Kdump: loaded Not tainted 6.4.0-150600.23.7-default #1 SLE15-SP6 ebc78bee233b1d2a183a14ef789e85be8041f896

[....]

[ xxxxxxx ] Krnl PSW : 0704e00180000000 000003ff8047caec (open_cached_dir+0x104/0x9c8 [cifs])
[ xxxxxxx ] Call Trace:
[ xxxxxxx ] [<000003ff8047caec>] open_cached_dir+0x104/0x9c8 [cifs]
[ xxxxxxx ] ([<000003ff8047ca9e>] open_cached_dir+0xb6/0x9c8 [cifs])
[ xxxxxxx ] [<000003ff804821f2>] cifs_readdir+0xab2/0x10c0 [cifs]

or

[ xxxxxxx ] CIFS: Attempting to mount //<IP>/cifs/share
[ xxxxxxx ] Unable to handle kernel pointer dereference in virtual kernel address space
...
[ xxxxxxx ] Oops: 0004 ilc:3 [#1] SMP

or 

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0 
Oops: 0000 [#1] PREEMPT SMP NOPTI
...
Call Trace:
? __die_body+0x1a/0x60
? page_fault_oops+0x131/0x510
? exc_page_fault+0x69/0x150
? asm_exc_page_fault+0x22/0x30
? strcmp+0x4/0x30
open_cached_dir+0x12f/0x9c0 [cifs 4bf515fd55be272b2b7f62ea07ad9bc4798fcc2f]

Resolution

The kernel update to version 6.4.0-150600.23.17.1 released August/2024 includes the patch to resolve the problem.

Cause

The cause of the issue is some missing spin_unlock() calls in open_cached_dir() which were omitted in a backported patch.

Status

Reported to Engineering

Disclaimer

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