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NFS: Prevent nfs_getattr() hang during heavy write workloads

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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>
This commit is contained in:
Chuck Lever 2007-10-26 13:32:13 -04:00 committed by Trond Myklebust
parent 464ad6b1ad
commit 28c494c5c8
1 changed files with 11 additions and 2 deletions
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13
fs/nfs/inode.c
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@ -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.