[Devel] [PATCH RHEL7 COMMIT] fuse: relax i_mutex coverage in fuse_fsync

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.36.1.vz7.20.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.36.1.vz7.20.7
------>
commit 9021a6d2234ad9e6b175e05286d9dc0018c19a85
Author: Maxim Patlasov <mpatlasov at virtuozzo.com>
Date:   Wed Nov 30 15:34:35 2016 +0400

    fuse: relax i_mutex coverage in fuse_fsync
    
    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 796638a..d11125f 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -704,6 +704,8 @@ 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;
@@ -722,6 +724,7 @@ 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;