From: Chuck Lever Date: Fri, 26 Oct 2007 17:32:13 +0000 (-0400) Subject: NFS: Prevent nfs_getattr() hang during heavy write workloads X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=28c494c5c8d425e15b7b82571e4df6d6bc34594d;p=openwrt%2Fstaging%2Fblogic.git 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 Signed-off-by: Trond Myklebust --- diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c index cd0e57f3a00f..cc3a09db41a9 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); nfs_wb_nocommit(inode); + mutex_unlock(&inode->i_mutex); + } /* * We may force a getattr if the user cares about atime.