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Mike Snitzer da729ddd4a NFS/localio: issue IO inline when not in a memory-reclaim context 
Every LOCALIO read and write is currently bounced through the dedicated
!WQ_MEM_RECLAIM nfslocaliod_workqueue.  That bounce is only actually
required when the submitting context is a memory-reclaim context: LOCALIO
issues IO directly into a stacked local filesystem (e.g. XFS) which may in
turn flush its own !WQ_MEM_RECLAIM workqueue.  Doing that from a
WQ_MEM_RECLAIM worker (most importantly writeback's wb_workfn on bdi_wq) or
an explicit PF_MEMALLOC reclaim task trips check_flush_dependency() and
risks a forward-progress deadlock, which is why commit b9f5dd57f4
("nfs/localio: use dedicated workqueues for filesystem read and write")
introduced the intermediate workqueue.

Outside of reclaim context -- ordinary application/task submission such as
O_DIRECT or fsync-driven writeback -- the workqueue hop buys nothing and
merely adds a context switch and scheduling latency per IO while discarding
the NFS client's inherent application-context parallelism.

Add current_is_workqueue_mem_reclaim(), which reports whether %current is a
WQ_MEM_RECLAIM worker using the same predicate check_flush_dependency()
warns on.  Use it, together with the PF_MEMALLOC check, in the new
nfs_local_defer_io() helper to decide per-IO whether nfs_local_do_read()
and nfs_local_do_write() must defer to nfslocaliod_workqueue or may issue
the IO inline.  Buffered writeback continues to bounce (wb_workfn is a
WQ_MEM_RECLAIM worker); O_DIRECT and app-context submission now run inline.

Running nfs_local_call_write() inline is safe: it already saves and
restores current->flags around the PF_LOCAL_THROTTLE|PF_MEMALLOC_NOIO it
sets and scopes the file opener's creds.  The async O_DIRECT completion
path is likewise unaffected: when the underlying filesystem returns
-EIOCBQUEUED, the kiocb ki_complete callback (nfs_local_read_aio_complete /
nfs_local_write_aio_complete) can run in bottom-half context and so must
still defer the pgio completion (nfs_local_pgio_release -> rpc_call_done) to
nfsiod_workqueue via nfs_local_pgio_aio_complete().  That completion hop is
independent of how the IO was submitted, and this change leaves it as-is;
only the submission side stops unconditionally hopping through
nfslocaliod_workqueue.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2026-08-17 09:02:07 -07:00
..
acpi ACPI: CPPC: Check all controls for fast switching 2026-07-22 15:09:14 +02:00
asm-generic mm.git review status for mm-hotfixes-stable..mm-nonmm-stable 2026-06-21 13:20:19 -07:00
clocksource
crypto Networking changes for 7.2. 2026-06-17 08:17:00 +01:00
cxl cxl/region: Introduce devm_cxl_probe_mem() 2026-06-12 13:47:30 -07:00
drm drm-misc-fixes for v7.2-rc5: 2026-07-24 18:30:29 +10:00
dt-bindings SoC fixes for 7.2 2026-07-17 08:52:09 -07:00
hyperv mshv: fix hv_input_get_system_property struct 2026-07-22 21:58:21 +00:00
keys keys: Pin request_key_auth payload in instantiate paths 2026-06-15 15:19:13 +03:00
kunit linux_kselftest-kunit-7.2-rc1 2026-06-16 16:33:57 +05:30
kvm KVM: arm64: vgic: Fix race between LPI release and re-registration 2026-07-23 09:56:57 +01:00
linux NFS/localio: issue IO inline when not in a memory-reclaim context 2026-08-17 09:02:07 -07:00
math-emu
media
memory
misc
net net/sched: reject overly deep qdisc hierarchies 2026-08-06 15:24:44 +02:00
pcmcia Replace <linux/mod_devicetable.h> by more specific <linux/device-id/*.h> (headers) 2026-07-03 07:38:16 +02:00
ras
rdma RDMA v7.2 merge window 2026-06-18 08:16:21 -07:00
rv
scsi SCSI fixes on 20260802 2026-08-02 09:32:07 -07:00
soc soc/tegra: pmc: Fixes for v7.2 2026-07-10 14:40:52 +02:00
sound ASoC/soundwire: Intel: reset the PCMSyCM registers in hda_sdw_bpt_close 2026-07-31 13:23:10 +01:00
target
trace for-7.2-rc6-fixup-worker-tag 2026-08-06 13:29:15 -07:00
uapi io_uring-7.2-20260724 2026-07-24 19:58:03 -07:00
ufs Merge branch 7.1/scsi-fixes into 7.2/scsi-staging 2026-06-15 21:01:30 -04:00
vdso
video
xen xen: Replace __ASSEMBLY__ with __ASSEMBLER__ in header files 2026-07-01 09:49:52 +02:00
Kbuild