[Devel] [PATCH vz7] fuse: relax i_mutex coverage in fuse_fsync

[Maxim Patlasov]

fuse_fsync_common() does need i_mutex for fuse_sync_writes() and
fuse_flush_mtime(). But when those operations are done, it's actually
doesn't matter whether to hold the lock over fuse_request_send(FUSE_FSYNC)
or not: we ensured that all relevant data were already seen by
userspace fuse daemon, and so it will sync them (by handling FUSE_FSYNC)
anyway; if the user screws up by leaking new data updates in-between, it
is up to the user and doesn't violate fsync(2) semantics.

https://jira.sw.ru/browse/PSBM-55919

Signed-off-by: Maxim Patlasov <mpatlasov at virtuozzo.com>
---
 fs/fuse/file.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 464b2f5..559dfd9 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -697,6 +697,8 @@ int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
 		goto out;
 	}
 
+	mutex_unlock(&inode->i_mutex);
+
 	memset(&inarg, 0, sizeof(inarg));
 	inarg.fh = ff->fh;
 	inarg.fsync_flags = datasync ? 1 : 0;
@@ -715,6 +717,7 @@ int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
 			fc->no_fsync = 1;
 		err = 0;
 	}
+	return err;
 out:
 	mutex_unlock(&inode->i_mutex);
 	return err;