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/[email protected]/
Cc: Alexander Viro <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: [email protected]
Cc: Nick Piggin <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: [email protected]
Signed-off-by: Vegard Nossum <[email protected]>
---
fs/dcache.c | 16 ++++------------
include/linux/dcache.h | 29 +++++++++++++++++++----------
2 files changed, 23 insertions(+), 22 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index c82ae731df9a..4bf33ba588d8 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;
}
@@ -1707,8 +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);
- *victim = dentry;
+ *victim = dget_dlock(dentry);
return D_WALK_QUIT;
}
return D_WALK_CONTINUE;
@@ -1853,8 +1846,7 @@ 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);
- dentry->d_parent = parent;
+ dentry->d_parent = dget_dlock(parent);
list_add(&dentry->d_child, &parent->d_subdirs);
spin_unlock(&parent->d_lock);
@@ -2851,7 +2843,7 @@ 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 3da2f0545d5d..82127cf10992 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -301,20 +301,29 @@ 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. For a dentry to be live, it can be hashed, positive,
+ * or have a non-negative &dentry->d_lockref.count
+ *
+ * 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)
@@ -325,10 +334,10 @@ 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)
--
2.34.1
[Fixed up a couple of bad addresses in Cc]
Hi,
I didn't get a response to this v2 of the patch below and I don't see it
in vfs.git.
Was there something wrong or is it just awaiting review? Is there
anything I can do or help with? I would be happy to try to review other
patches if there is anything outstanding.
Thanks,
Vegard
On 06/11/2023 14:44, Vegard Nossum wrote:
> 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/[email protected]/
> Cc: Alexander Viro <[email protected]>
> Cc: Christian Brauner <[email protected]>
> Cc: [email protected]
> Cc: Nick Piggin <[email protected]>
> Cc: Waiman Long <[email protected]>
> Cc: [email protected]
> Signed-off-by: Vegard Nossum <[email protected]>
> ---
> fs/dcache.c | 16 ++++------------
> include/linux/dcache.h | 29 +++++++++++++++++++----------
> 2 files changed, 23 insertions(+), 22 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index c82ae731df9a..4bf33ba588d8 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;
> }
> @@ -1707,8 +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);
> - *victim = dentry;
> + *victim = dget_dlock(dentry);
> return D_WALK_QUIT;
> }
> return D_WALK_CONTINUE;
> @@ -1853,8 +1846,7 @@ 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);
> - dentry->d_parent = parent;
> + dentry->d_parent = dget_dlock(parent);
> list_add(&dentry->d_child, &parent->d_subdirs);
> spin_unlock(&parent->d_lock);
>
> @@ -2851,7 +2843,7 @@ 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 3da2f0545d5d..82127cf10992 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -301,20 +301,29 @@ 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. For a dentry to be live, it can be hashed, positive,
> + * or have a non-negative &dentry->d_lockref.count
> + *
> + * 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)
> @@ -325,10 +334,10 @@ 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)
On Wed, Dec 13, 2023 at 03:40:33PM +0100, Vegard Nossum wrote:
> [Fixed up a couple of bad addresses in Cc]
>
> Hi,
>
> I didn't get a response to this v2 of the patch below and I don't see it
> in vfs.git.
>
> Was there something wrong or is it just awaiting review? Is there
> anything I can do or help with? I would be happy to try to review other
> patches if there is anything outstanding.
commit 1b6ae9f6e6c3e3c35aad0f11b116a81780b8aa03 (work.dcache)
Author: Vegard Nossum <[email protected]>
Date: Mon Nov 6 14:44:17 2023 +0100
dcache: remove unnecessary NULL check in dget_dlock()
On 13/12/2023 16:05, Al Viro wrote:
> On Wed, Dec 13, 2023 at 03:40:33PM +0100, Vegard Nossum wrote:
>> [Fixed up a couple of bad addresses in Cc]
>>
>> Hi,
>>
>> I didn't get a response to this v2 of the patch below and I don't see it
>> in vfs.git.
>>
>> Was there something wrong or is it just awaiting review? Is there
>> anything I can do or help with? I would be happy to try to review other
>> patches if there is anything outstanding.
>
> commit 1b6ae9f6e6c3e3c35aad0f11b116a81780b8aa03 (work.dcache)
> Author: Vegard Nossum <[email protected]>
> Date: Mon Nov 6 14:44:17 2023 +0100
>
> dcache: remove unnecessary NULL check in dget_dlock()
>
Ahh, there are two vfs.git -- my bad. Thanks!
Vegard