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Message-Id: <20231022164520.915013-1-vegard.nossum@oracle.com>
Date: Sun, 22 Oct 2023 18:45:20 +0200
From: Vegard Nossum <vegard.nossum@...cle.com>
To: Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>
Cc: linux-kernel@...r.kernel.org,
Vegard Nossum <vegard.nossum@...cle.com>,
linux-fsdevel@...r.kernel.org, Nick Piggin <npiggin@...nel.dk>,
Waiman Long <Waiman.Long@...com>, linux-doc@...r.kernel.org
Subject: [PATCH] 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.
Testing: x86 defconfig build + boot; make htmldocs for the kerneldoc
warning. objdump shows there are code generation changes.
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org
Cc: Nick Piggin <npiggin@...nel.dk>
Cc: Waiman Long <Waiman.Long@...com>
Cc: linux-doc@...r.kernel.org
Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
---
fs/dcache.c | 14 ++++----------
include/linux/dcache.h | 20 ++++++++++++++------
2 files changed, 18 insertions(+), 16 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 25ac74d30bff..8c3c0d691605 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -942,12 +942,6 @@ void dput_to_list(struct dentry *dentry, struct list_head *list)
spin_unlock(&dentry->d_lock);
}
-/* This must be called with d_lock held */
-static inline void __dget_dlock(struct dentry *dentry)
-{
- dentry->d_lockref.count++;
-}
-
static inline void __dget(struct dentry *dentry)
{
lockref_get(&dentry->d_lockref);
@@ -1034,7 +1028,7 @@ static struct dentry *__d_find_alias(struct inode *inode)
hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
spin_lock(&alias->d_lock);
if (!d_unhashed(alias)) {
- __dget_dlock(alias);
+ dget_dlock(alias);
spin_unlock(&alias->d_lock);
return alias;
}
@@ -1707,7 +1701,7 @@ static enum d_walk_ret find_submount(void *_data, struct dentry *dentry)
{
struct dentry **victim = _data;
if (d_mountpoint(dentry)) {
- __dget_dlock(dentry);
+ dget_dlock(dentry);
*victim = dentry;
return D_WALK_QUIT;
}
@@ -1853,7 +1847,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
* don't need child lock because it is not subject
* to concurrency here
*/
- __dget_dlock(parent);
+ dget_dlock(parent);
dentry->d_parent = parent;
list_add(&dentry->d_child, &parent->d_subdirs);
spin_unlock(&parent->d_lock);
@@ -2851,7 +2845,7 @@ struct dentry *d_exact_alias(struct dentry *entry, struct inode *inode)
spin_unlock(&alias->d_lock);
alias = NULL;
} else {
- __dget_dlock(alias);
+ dget_dlock(alias);
__d_rehash(alias);
spin_unlock(&alias->d_lock);
}
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 6b351e009f59..e22f1520ea3b 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -300,20 +300,28 @@ extern char *dentry_path(const struct dentry *, char *, int);
/* Allocation counts.. */
/**
- * dget, dget_dlock - get a reference to a dentry
+ * 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 dentry, increment the reference count and return the
+ * dentry.
+ *
+ * Context: @dentry->d_lock must be held.
*/
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.
+ */
static inline struct dentry *dget(struct dentry *dentry)
{
if (dentry)
--
2.34.1
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