Messages in this thread | | | Date | Thu, 21 Nov 2013 15:01:07 -0800 | From | Greg KH <> | Subject | Re: 3.12 Regression: dcache: Translating dentry into pathname without taking rename_lock 232d2d60 |
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On Wed, Nov 13, 2013 at 02:51:59PM -0800, Michael Marineau wrote: > On Wed, Nov 13, 2013 at 4:39 AM, Al Viro <viro@zeniv.linux.org.uk> wrote: > > On Wed, Nov 13, 2013 at 03:34:13AM -0800, Michael Marineau wrote: > >> Greetings, > >> > >> Commit 232d2d60aa5469bb097f55728f65146bd49c1d25 causes intermittent > >> errors in /proc/*/fd/* where readlink returns "/" instead of the > >> correct path. This can be reproduced by the script below which copies > >> the kernel source directory structure while obsessively looking up > >> directory fds in proc from another process. Reverting > >> 232d2d60aa5469bb097f55728f65146bd49c1d25 after two related commits > >> 48f5ec21d9c67e881ff35343988e290ef5cf933f > >> 1812997720ab90d029548778c55d7315555e1fef fixes the issue. > > > > Looking into it... It seems that we are getting to the end of > > prepend_path() with non-negative error and bptr == *buffer. > > What the... > > > > OK, I see what's going on. We never reinitialize dentry, vfsmount and mnt > > if we decide to restart. See if the following helps: > > > > diff --git a/fs/dcache.c b/fs/dcache.c > > index ae6ebb8..89f9671 100644 > > --- a/fs/dcache.c > > +++ b/fs/dcache.c > > @@ -2881,9 +2881,9 @@ static int prepend_path(const struct path *path, > > const struct path *root, > > char **buffer, int *buflen) > > { > > - struct dentry *dentry = path->dentry; > > - struct vfsmount *vfsmnt = path->mnt; > > - struct mount *mnt = real_mount(vfsmnt); > > + struct dentry *dentry; > > + struct vfsmount *vfsmnt; > > + struct mount *mnt; > > int error = 0; > > unsigned seq = 0; > > char *bptr; > > @@ -2893,6 +2893,9 @@ static int prepend_path(const struct path *path, > > restart: > > bptr = *buffer; > > blen = *buflen; > > + dentry = path->dentry; > > + vfsmnt = path->mnt; > > + mnt = real_mount(vfsmnt); > > read_seqbegin_or_lock(&rename_lock, &seq); > > while (dentry != root->dentry || vfsmnt != root->mnt) { > > struct dentry * parent; > > That appears to do the trick! I've tried my test case against that > patch on both Linus' git tree (as of last night) and the 3.12 release. > I'm now running the long build job that initially stumbled across this > bug now but it looks good so far.
Al, did this fix end up in Linus's tree yet? I'd like to pull it into the next 3.12-stable release, but will wait until Linus has it of course.
thanks,
greg k-h
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