[PATCHv3 0/1] xfs: soft lockups in unmapping and reflink remapping path

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

Hello,

In one of the testcases, parallel async dio writes to a file generates
large no. of extents (upto 2M or more), and then this file is cleaned up for
running other I/O tests. In the process of deleting this file, soft lockup
messages are observed. We believe this is happening due to kernel being busy
in unmapping/freeing those extents as part of the transaction processing.
This is similar observation with the same call stack which was also reported
here [1]. I also tried the qemu-img bench testcase shared in [1], and I was
able to reproduce the soft lockup with that on Power.

Similarly another instance was reported where xfs reflink remapping path also
saw a similar softlockup problem while iterating over deferrd work items
in xfs_trans_commit() -> xfs_defer_finish_noroll().

So as I understood from that discussion [1], that kernel is moving towards a new
preemption model, but IIUC, it is still an ongoing work.
Also IMHO, this is still a problem in upstream and in older stable kernels
which we still do support and such a fix might still be necessary for them.

This patch fixes the softlockup warning for both of the callstacks.

v2 -> v3:
Move cond_resched within xfs_defer_finish_noroll() loop

[v2]: https://lore.kernel.org/linux-xfs/cover.1714033516.git.ritesh.list@gmail.com/

Ritesh Harjani (IBM) (1):
  xfs: Add cond_resched to xfs_defer_finish_noroll

 fs/xfs/libxfs/xfs_defer.c | 1 +
 1 file changed, 1 insertion(+)

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2.44.0