[SRU][jammy PATCH v2 0/1] NFS: fix deadlock with pNFS flexfiles IO retry error path

[Mike Snitzer]

BugLink: https://bugs.launchpad.net/bugs/2089410

SRU Justification:
Impact: In production at a mutual "hyperscaler" customer that is using
the Ubuntu jammy kernel's NFS client with Hammerspace's pNFS
flexfiles: NFS client deadlock occurred due to upstream commit
7be7b3ca16a59 ("NFS: Ensure we immediately start writeback on
rescheduled writes"). Which was later fixed with upstream commit
b1a28f2eb9ea7 ("NFS: nfs_async_write_reschedule_io must not recurse
into the writeback code") in August 2022. But it unfortunately wasn't
marked for stable@ at that time. That has since been rectified and
Greg Kroah-Hartman has now picked it up for the next
stable/linux-5.15.y kernel (but it hasn't yet appeared in the stable
repo), please see:
https://lore.kernel.org/stable/2024112146-tiptoeing-available-c5fe@gregkh/T/

Fix:
Apply upstream commit b1a28f2eb9ea7 ("NFS:
nfs_async_write_reschedule_io must not recurse into the writeback
code"), that commit was developed by and came from Trond Myklebust the
upstream Linux NFS client maintainer.

Testcase:
Cause buffered IO issued by NFS client using pNFS flexfiles to hit
error paths (due to heavy enterprise use, with container limits being
imposed, which makes OOM within container particularly prone to hit
error memory allocation errors _and_ additional reason for NFS IO to
be retransmitted, e.g. due to volume down/up bounces). This can lead
to deadlock in NFS due to recursion with page locks already held,
e.g.:
[<0>] wait_on_page_bit_common+0x10c/0x3d0
[<0>] wait_on_page_bit+0x3f/0x50
[<0>] wait_on_page_writeback+0x26/0x80
[<0>] write_cache_pages+0x138/0x460
[<0>] nfs_writepages+0x10d/0x200 [nfs]
[<0>] do_writepages+0xd4/0x200
[<0>] filemap_fdatawrite_wbc+0x89/0xe0
[<0>] filemap_fdatawrite_range+0x54/0x70
[<0>] nfs_async_write_reschedule_io+0x69/0x80 [nfs]
[<0>] ff_layout_reset_write+0x73/0xe0 [nfs_layout_flexfiles]
[<0>] ff_layout_write_release+0x7a/0x90 [nfs_layout_flexfiles]
[<0>] rpc_free_task+0x3d/0x70 [sunrpc]
[<0>] rpc_async_release+0x30/0x50 [sunrpc]
[<0>] process_one_work+0x228/0x3d0
[<0>] worker_thread+0x53/0x420
[<0>] kthread+0x127/0x150
[<0>] ret_from_fork+0x1f/0x30

Trond Myklebust (1):
  NFS: nfs_async_write_reschedule_io must not recurse into the writeback code

 fs/nfs/write.c | 2 --
 1 file changed, 2 deletions(-)

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2.44.0