public-mirrors/linux
1
0
Fork 0
mirror of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2025-08-05 16:54:27 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

ovl: narrow locking in ovl_whiteout()

Browse source 
ovl_whiteout() relies on the workdir i_rwsem to provide exclusive access
to ofs->whiteout which it manipulates.  Rather than depending on this,
add a new mutex, "whiteout_lock" to explicitly provide the required
locking.  Use guard(mutex) for this so that we can return without
needing to explicitly unlock.

Then take the lock on workdir only when needed - to lookup the temp name
and to do the whiteout or link.

Signed-off-by: NeilBrown <neil@brown.name>
Link: https://lore.kernel.org/20250716004725.1206467-19-neil@brown.name
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
NeilBrown 2025-07-16 10:44:29 +10:00 • committed by Christian Brauner
parent 2fa14cf2dc
commit 8afa0a7367
No known key found for this signature in database
GPG key ID: 91C61BC06578DCA2
3 changed files with 28 additions and 21 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

46
fs/overlayfs/dir.c
View file

@ -84,41 +84,45 @@ static struct dentry *ovl_whiteout(struct ovl_fs *ofs)
struct dentry *workdir = ofs->workdir;
struct inode *wdir = workdir->d_inode;
inode_lock_nested(wdir, I_MUTEX_PARENT);
if (!ofs->whiteout) {
whiteout = ovl_lookup_temp(ofs, workdir);
if (IS_ERR(whiteout))
goto out;
guard(mutex)(&ofs->whiteout_lock);
err = ovl_do_whiteout(ofs, wdir, whiteout);
if (err) {
dput(whiteout);
whiteout = ERR_PTR(err);
goto out;
if (!ofs->whiteout) {
inode_lock_nested(wdir, I_MUTEX_PARENT);
whiteout = ovl_lookup_temp(ofs, workdir);
if (!IS_ERR(whiteout)) {
err = ovl_do_whiteout(ofs, wdir, whiteout);
if (err) {
dput(whiteout);
whiteout = ERR_PTR(err);
}
}
inode_unlock(wdir);
if (IS_ERR(whiteout))
return whiteout;
ofs->whiteout = whiteout;
}
if (!ofs->no_shared_whiteout) {
inode_lock_nested(wdir, I_MUTEX_PARENT);
whiteout = ovl_lookup_temp(ofs, workdir);
if (IS_ERR(whiteout))
goto out;
err = ovl_do_link(ofs, ofs->whiteout, wdir, whiteout);
if (!err)
goto out;
if (err != -EMLINK) {
if (!IS_ERR(whiteout)) {
err = ovl_do_link(ofs, ofs->whiteout, wdir, whiteout);
if (err) {
dput(whiteout);
whiteout = ERR_PTR(err);
}
}
inode_unlock(wdir);
if (!IS_ERR(whiteout))
return whiteout;
if (PTR_ERR(whiteout) != -EMLINK) {
pr_warn("Failed to link whiteout - disabling whiteout inode sharing(nlink=%u, err=%i)\n",
ofs->whiteout->d_inode->i_nlink, err);
ofs->no_shared_whiteout = true;
}
dput(whiteout);
}
whiteout = ofs->whiteout;
ofs->whiteout = NULL;
out:
inode_unlock(wdir);
return whiteout;
}

1
fs/overlayfs/ovl_entry.h
View file

@ -88,6 +88,7 @@ struct ovl_fs {
/* Shared whiteout cache */
struct dentry *whiteout;
bool no_shared_whiteout;
struct mutex whiteout_lock;
/* r/o snapshot of upperdir sb's only taken on volatile mounts */
errseq_t errseq;
};

2
fs/overlayfs/params.c
View file

@ -795,6 +795,8 @@ int ovl_init_fs_context(struct fs_context *fc)
fc->s_fs_info = ofs;
fc->fs_private = ctx;
fc->ops = &ovl_context_ops;
mutex_init(&ofs->whiteout_lock);
return 0;
out_err: