Al, Thank a lot for quickly locating the bug.
-Longman -----Original Message----- From: Al Viro [mailto:[email protected]] On Behalf Of Al Viro Sent: Wednesday, November 13, 2013 7:40 AM To: Michael Marineau Cc: Long, Wai Man; [email protected] Subject: Re: 3.12 Regression: dcache: Translating dentry into pathname without taking rename_lock 232d2d60 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
