Commit 28c494c5 authored Oct 26, 2007 by Chuck Lever Committed by Trond Myklebust Jan 30, 2008

NFS: Prevent nfs_getattr() hang during heavy write workloads

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 <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

parent 464ad6b1

fs/nfs/inode.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -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);
		nfs_wb_nocommit(inode);
		mutex_unlock(&inode->i_mutex);
		}

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