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authorVegard Nossum <vegard.nossum@oracle.com>2023-11-06 16:44:17 +0300
committerAl Viro <viro@zeniv.linux.org.uk>2023-11-25 10:51:56 +0300
commit1b6ae9f6e6c3e3c35aad0f11b116a81780b8aa03 (patch)
tree77a46a9d530844b6e6ea971c3f2b63ef9d0084b9 /include/linux/dcache.h
parent1b327b5ac57cf83e3d015de45d0142852f475375 (diff)
downloadlinux-1b6ae9f6e6c3e3c35aad0f11b116a81780b8aa03.tar.xz
dcache: remove unnecessary NULL check in dget_dlock()
dget_dlock() requires dentry->d_lock to be held when called, yet contains a NULL check for dentry. An audit of all calls to dget_dlock() shows that it is never called with a NULL pointer (as spin_lock()/spin_unlock() would crash in these cases): $ git grep -W '\<dget_dlock\>' arch/powerpc/platforms/cell/spufs/inode.c- spin_lock(&dentry->d_lock); arch/powerpc/platforms/cell/spufs/inode.c- if (simple_positive(dentry)) { arch/powerpc/platforms/cell/spufs/inode.c: dget_dlock(dentry); fs/autofs/expire.c- spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED); fs/autofs/expire.c- if (simple_positive(child)) { fs/autofs/expire.c: dget_dlock(child); fs/autofs/root.c: dget_dlock(active); fs/autofs/root.c- spin_unlock(&active->d_lock); fs/autofs/root.c: dget_dlock(expiring); fs/autofs/root.c- spin_unlock(&expiring->d_lock); fs/ceph/dir.c- if (!spin_trylock(&dentry->d_lock)) fs/ceph/dir.c- continue; [...] fs/ceph/dir.c: dget_dlock(dentry); fs/ceph/mds_client.c- spin_lock(&alias->d_lock); [...] fs/ceph/mds_client.c: dn = dget_dlock(alias); fs/configfs/inode.c- spin_lock(&dentry->d_lock); fs/configfs/inode.c- if (simple_positive(dentry)) { fs/configfs/inode.c: dget_dlock(dentry); fs/libfs.c: found = dget_dlock(d); fs/libfs.c- spin_unlock(&d->d_lock); fs/libfs.c: found = dget_dlock(child); fs/libfs.c- spin_unlock(&child->d_lock); fs/libfs.c: child = dget_dlock(d); fs/libfs.c- spin_unlock(&d->d_lock); fs/ocfs2/dcache.c: dget_dlock(dentry); fs/ocfs2/dcache.c- spin_unlock(&dentry->d_lock); include/linux/dcache.h:static inline struct dentry *dget_dlock(struct dentry *dentry) After taking out the NULL check, dget_dlock() becomes almost identical to __dget_dlock(); the only difference is that dget_dlock() returns the dentry that was passed in. These are static inline helpers, so we can rely on the compiler to discard unused return values. We can therefore also remove __dget_dlock() and replace calls to it by dget_dlock(). Also fix up and improve the kerneldoc comments while we're at it. Al Viro pointed out that we can also clean up some of the callers to make use of the returned value and provided a bit more info for the kerneldoc. While preparing v2 I also noticed that the tabs used in the kerneldoc comments were causing the kerneldoc to get parsed incorrectly so I also fixed this up (including for d_unhashed, which is otherwise unrelated). Testing: x86 defconfig build + boot; make htmldocs for the kerneldoc warning. objdump shows there are code generation changes. Link: https://lore.kernel.org/all/20231022164520.915013-1-vegard.nossum@oracle.com/ Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: linux-fsdevel@vger.kernel.org Cc: Nick Piggin <npiggin@kernel.dk> Cc: Waiman Long <Waiman.Long@hp.com> Cc: linux-doc@vger.kernel.org Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'include/linux/dcache.h')
-rw-r--r--include/linux/dcache.h41
1 files changed, 30 insertions, 11 deletions
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 48b393545ec2..1666c387861f 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -287,20 +287,40 @@ extern char *dentry_path(const struct dentry *, char *, int);
/* Allocation counts.. */
/**
- * dget, dget_dlock - get a reference to a dentry
- * @dentry: dentry to get a reference to
+ * dget_dlock - get a reference to a dentry
+ * @dentry: dentry to get a reference to
*
- * Given a dentry or %NULL pointer increment the reference count
- * if appropriate and return the dentry. A dentry will not be
- * destroyed when it has references.
+ * Given a live dentry, increment the reference count and return the dentry.
+ * Caller must hold @dentry->d_lock. Making sure that dentry is alive is
+ * caller's resonsibility. There are many conditions sufficient to guarantee
+ * that; e.g. anything with non-negative refcount is alive, so's anything
+ * hashed, anything positive, anyone's parent, etc.
*/
static inline struct dentry *dget_dlock(struct dentry *dentry)
{
- if (dentry)
- dentry->d_lockref.count++;
+ dentry->d_lockref.count++;
return dentry;
}
+
+/**
+ * dget - get a reference to a dentry
+ * @dentry: dentry to get a reference to
+ *
+ * Given a dentry or %NULL pointer increment the reference count
+ * if appropriate and return the dentry. A dentry will not be
+ * destroyed when it has references. Conversely, a dentry with
+ * no references can disappear for any number of reasons, starting
+ * with memory pressure. In other words, that primitive is
+ * used to clone an existing reference; using it on something with
+ * zero refcount is a bug.
+ *
+ * NOTE: it will spin if @dentry->d_lock is held. From the deadlock
+ * avoidance point of view it is equivalent to spin_lock()/increment
+ * refcount/spin_unlock(), so calling it under @dentry->d_lock is
+ * always a bug; so's calling it under ->d_lock on any of its descendents.
+ *
+ */
static inline struct dentry *dget(struct dentry *dentry)
{
if (dentry)
@@ -311,12 +331,11 @@ static inline struct dentry *dget(struct dentry *dentry)
extern struct dentry *dget_parent(struct dentry *dentry);
/**
- * d_unhashed - is dentry hashed
- * @dentry: entry to check
+ * d_unhashed - is dentry hashed
+ * @dentry: entry to check
*
- * Returns true if the dentry passed is not currently hashed.
+ * Returns true if the dentry passed is not currently hashed.
*/
-
static inline int d_unhashed(const struct dentry *dentry)
{
return hlist_bl_unhashed(&dentry->d_hash);