[PATCH 1/2] NFSD: Fix duplicate fsnotify access events for iterator READs

A READ served without splice emits two fsnotify access events; a
local read of the same file emits one. vfs_iocb_iter_read() emits
an access event when the read succeeds, and nfsd_finish_read()
emits a second one for the same READ. An inotify watch on an
exported file sees each of these READs twice, so anything counting
accesses counts double. READs take this path whenever nfsd does
not use splice, for example with sec=krb5i or sec=krb5p, or when
nfsd_disable_splice_read is set, as the NFSD_IO_DONTCACHE and
NFSD_IO_DIRECT modes do. Spliced READs are not affected, since
splice_direct_to_actor() emits no event and nfsd_finish_read()
emits their only one.

Move the fsnotify_access() call from nfsd_finish_read() into
nfsd_splice_read(), the one path whose VFS helper does not emit
it. Each READ now emits exactly one access event whichever path
serves it. Measured with an inotify watch: the iterator path drops
from two events per READ to one, and the splice path is unchanged
at one.

Suggested-by: Chuck Lever <[email protected]>
Link: https://lore.kernel.org/linux-nfs/[email protected]/
Fixes: 507df40ebf316 ("NFSD: Hoist rq_vec preparation into nfsd_read()")
Cc: [email protected]
Assisted-by: Claude:claude-fable-5
Signed-off-by: Ameer Hamza <[email protected]>
---
 fs/nfsd/vfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index f9131827d391e..f45d4ad70b964 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1046,7 +1046,6 @@ static __be32 nfsd_finish_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		nfsd_stats_io_read_add(nn, fhp->fh_export, host_err);
 		*eof = nfsd_eof_on_read(file, offset, host_err, *count);
 		*count = host_err;
-		fsnotify_access(file);
 		trace_nfsd_read_io_done(rqstp, fhp, offset, *count);
 		return 0;
 	} else {
@@ -1084,6 +1083,9 @@ __be32 nfsd_splice_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (!host_err)
 		host_err = splice_direct_to_actor(file, &sd,
 						  nfsd_direct_splice_actor);
+	/* splice_direct_to_actor() does not emit an fsnotify event */
+	if (host_err >= 0)
+		fsnotify_access(file);
 	return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_err);
 }
 

base-commit: c5f58d03c50196301ac2ce7da81e8be33eba57c6
-- 
2.53.0