Attachment 246911 Details for Bug 364351 – patch -- discard pagecahe for dirs on dentry iput

[patch] patch -- discard pagecahe for dirs on dentry iput

0020-BZ-327591-NFS-discard-pagecache-data-for-dirs-on-d.patch (text/plain), 3.30 KB, created by Jeff Layton on 2007-11-02 17:55:41 UTC

(hide)

Description:

Filename:

MIME Type:

Creator: Jeff Layton

Created: 2007-11-02 17:55:41 UTC

Size: 3.30 KB

patch

obsolete

>From c686036444a472ef804ef67eeee8f06310247abf Mon Sep 17 00:00:00 2001
>From: Neil Brown <neilb@suse.de>
>Date: Mon, 26 Feb 2007 12:48:25 +1100
>Subject: [PATCH] BZ#327591: NFS: discard pagecache data for dirs on dentry_iput
>
>Try running this script in an NFS mounted directory (Client relatively
>recent - 2.6.18 has the problem as does 2.6.20).
>
>------------------------------------------------------
>
>rm -rf nfstest
>mkdir -p nfstest/dir/innerdir
>
>echo "Hello World!" >nfstest/dir/file
>echo "Hello World!" >nfstest/dir/innerdir/innerfile
>
>sleep 1
>
>chmod -R a+r nfstest
>
>mv nfstest/dir nfstest/newdir
>
>tar -cf nfstest/nfstest.tar -C nfstest newdir
>
>mv nfstest/newdir nfstest/dir
>--------------------------------------------------------
>
>What happens:
>
>The 'chmod -R' does a readdir_plus in each directory and the results
>get cached in the page cache.  It then updates the ctime on each file
>by one second.  When this happens, the post-op attributes are used to
>update the ctime stored on the client to match the value in the kernel.
>
>The 'mv' calls shrink_dcache_parent on the directory tree which
>flushes all the dentries (so a new lookup will be required) but
>doesn't flush the inodes or pagecache.
>
>The 'tar' does a readdir on each directory, but (in the case of
>'innerdir' at least) satisfies it from the pagecache and uses the
>READDIRPLUS data to update all the inodes.  In the case of
>'innerdir/innerfile', the ctime is out of date.
>
>'tar' then calls 'lstat' on innerdir/innerfile getting an old ctime.
>It then opens the file (triggering a GETATTR), reads the content, and
>then calls fstat to see if anything has changed.  It finds that ctime
>has changed and so complains.
>
>The problem seems to be that the cache readdirplus info is kept around
>for too long.
>
>My patch below discards pagecache data for directories when
>dentry_iput is called on them.  This effectively removes the symptom
>which convinces me that I correctly understand the problem.  However
>I'm not convinced that is a proper solution, as there could easily be
>other races that trigger the same problem without being affected by
>this 'fix'.
>
>One possibility would be to require that readdirplus pagecache data be
>only used *once* to instantiate an inode.  Somehow it should then be
>invalidated so that if the dentry subsequently disappears, it will
>cause a new request to the server to fill in the stat data.
>
>Another possibility is to compare the cache_change_attribute on the
>inode with something similar for the readdirplus info and reject the
>info from readdirplus if it is too old.
>
>I haven't tried to implement these and would value other opinions
>before I do.
>
>Thanks,
>NeilBrown
>
>Signed-off-by: Neil Brown <neilb@suse.de>
>Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
>---
> fs/nfs/dir.c |    4 ++++
> 1 files changed, 4 insertions(+), 0 deletions(-)
>
>diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
>index 4f4a11a..0fa248a 100644
>--- a/fs/nfs/dir.c
>+++ b/fs/nfs/dir.c
>@@ -822,6 +822,10 @@ static int nfs_dentry_delete(struct dentry *dentry)
> static void nfs_dentry_iput(struct dentry *dentry, struct inode *inode)
> {
> 	nfs_inode_return_delegation(inode);
>+	if (S_ISDIR(inode->i_mode))
>+		/* drop any readdir cache as it could easily be old */
>+		NFS_I(inode)->cache_validity |= NFS_INO_INVALID_DATA;
>+
> 	if (dentry->d_flags & DCACHE_NFSFS_RENAMED) {
> 		lock_kernel();
> 		inode->i_nlink--;
>-- 
>1.5.3.3
>

Actions: View | Diff

Attachments on bug 364351: 246911