kernel BUG at ../drivers/md/bcache/bset.c:884

This document (000020355) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server for SAP 15 SP2

Situation

This issue was noticed when using bcache for cache acceleration of SAP HANA data disks.
The following was seen in /var/log/messages:

xy1d kernel: [721646.767939] ------------[ cut here ]------------ 
xy1d kernel: [721646.767942] kernel BUG at ../drivers/md/bcache/bset.c:884! 
xy1d kernel: [721646.767950] invalid opcode: 0000 [#1] SMP NOPTI
xy1d kernel: [721646.767962] CPU: 309 PID: 217475 Comm: SubmitThread-DA Tainted: G             L X    5.3.18-24.52-default #1 SLE15-SP2
xy1d kernel: [721646.767966] Hardware name: Inspur TS860M5/YZCP-00916-101, BIOS 4.1.16 09/10/2020
xy1d kernel: [721646.767989] RIP: 0010:bch_btree_insert_key+0x28c/0x2b0 [bcache]

In addition SAP HANA hung during shutdown process.
Currently it was only seen on the hardware mentioned above. Other hardware may be affected, too.

Resolution

On SLES15SP2 this issue is fixed with kernel-default-5.3.18-24.78.1.

If a reboot is not possible immediately kernel-livepatch-SLE15-SP2_Update_18-1-5.3.1 may be installed (requires extra Kernel Livepatching Subscription)

SLES15 SP3 was released with a fixed kernel.
The systemd unit mentioned below may still be required.

Status

Reported to Engineering

Additional Information

There may be situations where SAP HANA hangs during system shutdown when using bcache.
This is caused by a race condition where the bcache device vanishes before the cache is written back completely. This leads to cache corruption and bcache needs to be reinitialized before next usage.
Upstream bug pending.

To mitigate SUSE Technical Support can provide a systemd unit to stop bcache safely before reboot. This can also be shared upon request.

Disclaimer

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