2008-01-25 16:59:50

by Myklebust, Trond

[permalink] [raw]
Subject: [PATCH 041/112] NFS: Prevent nfs_getattr() hang during heavy write workloads

From: Chuck Lever <[email protected]>

POSIX requires that ctime and mtime, as reported by the stat(2) call,
reflect the activity of the most recent write(2). To that end, nfs_getattr()
flushes pending dirty writes to a file before doing a GETATTR to allow the
NFS server to set the file's size, ctime, and mtime properly.

However, nfs_getattr() can be starved when a constant stream of application
writes to a file prevents nfs_wb_nocommit() from completing. This usually
results in hangs of programs doing a stat against an NFS file that is being
written. "ls -l" is a common victim of this behavior.

To prevent starvation, hold the file's i_mutex in nfs_getattr() to
freeze applications writes temporarily so the client can more quickly obtain
clean values for a file's size, mtime, and ctime.

Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: Trond Myklebust <[email protected]>

fs/nfs/inode.c | 13 +++++++++++--
1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index cd0e57f..cc3a09d 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -461,9 +461,18 @@ int nfs_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
int need_atime = NFS_I(inode)->cache_validity & NFS_INO_INVALID_ATIME;
int err;

- /* Flush out writes to the server in order to update c/mtime */
- if (S_ISREG(inode->i_mode))
+ /*
+ * Flush out writes to the server in order to update c/mtime.
+ *
+ * Hold the i_mutex to suspend application writes temporarily;
+ * this prevents long-running writing applications from blocking
+ * nfs_wb_nocommit.
+ */
+ if (S_ISREG(inode->i_mode)) {
+ mutex_lock(&inode->i_mutex);
+ mutex_unlock(&inode->i_mutex);
+ }

* We may force a getattr if the user cares about atime.