From 28c494c5c8d425e15b7b82571e4df6d6bc34594d Mon Sep 17 00:00:00 2001
From: Chuck Lever <chuck.lever@oracle.com>
Date: Fri, 26 Oct 2007 13:32:13 -0400
Subject: [PATCH] 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>
---
fs/nfs/inode.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
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.
--
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