diff options
| author | NeilBrown <neil@brown.name> | 2025-07-16 10:44:29 +1000 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2025-07-18 11:10:42 +0200 |
| commit | 8afa0a736713898f04d52abad69c07caa2c2f227 (patch) | |
| tree | 68ed8d2a478e5ce3428d8aeb4f94b9ce28321f82 | |
| parent | 2fa14cf2dca1913054e0225377d0a9999483d34d (diff) | |
ovl: narrow locking in ovl_whiteout()
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>
| -rw-r--r-- | fs/overlayfs/dir.c | 44 | ||||
| -rw-r--r-- | fs/overlayfs/ovl_entry.h | 1 | ||||
| -rw-r--r-- | fs/overlayfs/params.c | 2 |
3 files changed, 27 insertions, 20 deletions
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index 6a70faeee6fa..7eb806a4e5f8 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -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); + guard(mutex)(&ofs->whiteout_lock); + if (!ofs->whiteout) { + inode_lock_nested(wdir, I_MUTEX_PARENT); whiteout = ovl_lookup_temp(ofs, workdir); - if (IS_ERR(whiteout)) - goto out; - - err = ovl_do_whiteout(ofs, wdir, whiteout); - if (err) { - dput(whiteout); - whiteout = ERR_PTR(err); - goto out; + 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; } diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h index afb7762f873f..4c1bae935ced 100644 --- a/fs/overlayfs/ovl_entry.h +++ b/fs/overlayfs/ovl_entry.h @@ -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; }; diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c index 2b9b31524c38..f4e7fff909ac 100644 --- a/fs/overlayfs/params.c +++ b/fs/overlayfs/params.c @@ -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: |