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Message-Id: <20220614020840.546013-4-imran.f.khan@oracle.com>
Date: Tue, 14 Jun 2022 12:08:39 +1000
From: Imran Khan <imran.f.khan@...cle.com>
To: tj@...nel.org, gregkh@...uxfoundation.org, viro@...iv.linux.org.uk
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH v5 3/4] kernfs: Introduce interface to access global kernfs_open_file_mutex.
This allows to change underlying mutex locking, without needing to change
the users of the lock. For example next patch modifies this interface to
use hashed mutexes in place of a single global kernfs_open_file_mutex.
Signed-off-by: Imran Khan <imran.f.khan@...cle.com>
Acked-by: Tejun Heo <tj@...nel.org>
---
fs/kernfs/file.c | 60 ++++++++++++++++++++++++++++++++----------------
1 file changed, 40 insertions(+), 20 deletions(-)
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 0cc288dcf51d9..205b5c71f30cb 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -49,6 +49,22 @@ struct kernfs_open_node {
static LLIST_HEAD(kernfs_notify_list);
+static inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node *kn)
+{
+ return &kernfs_open_file_mutex;
+}
+
+static inline struct mutex *kernfs_open_file_mutex_lock(struct kernfs_node *kn)
+{
+ struct mutex *lock;
+
+ lock = kernfs_open_file_mutex_ptr(kn);
+
+ mutex_lock(lock);
+
+ return lock;
+}
+
/**
* kernfs_deref_open_node - Get kernfs_open_node corresponding to @kn.
*
@@ -56,7 +72,7 @@ static LLIST_HEAD(kernfs_notify_list);
* @kn: target kernfs_node.
*
* Fetch and return ->attr.open of @kn if @of->list is not empty or if
- * kernfs_open_file_mutex is held.
+ * kernfs_open_file_mutex_ptr(kn) is held.
*
* We can rely on either of the following 2 conditions to ensure that
* dereferencing ->attr.open outside RCU read-side critical section is safe.
@@ -68,13 +84,13 @@ static LLIST_HEAD(kernfs_notify_list);
*
* or
*
- * 2. Update of ->attr.open happens under kernfs_open_file_mutex. So as long as
- * the current updater (caller) is holding this mutex, other updaters will not
- * be able to change ->attr.open and this means that we can safely deref
- * ->attr.open outside RCU read-side critical section.
+ * 2. Update of ->attr.open happens under kernfs_open_file_mutex_ptr(kn). So as
+ * long as the current updater (caller) holds this mutex, other updaters can't
+ * change ->attr.open and this means that we can safely deref ->attr.open
+ * outside RCU read-side critical section.
*
* The caller needs to make sure that either @of->list is not empty or
- * kernfs_open_file_mutex is held.
+ * kernfs_open_file_mutex_ptr(kn) is held.
*/
static struct kernfs_open_node *
kernfs_deref_open_node(struct kernfs_open_file *of, struct kernfs_node *kn)
@@ -83,7 +99,7 @@ kernfs_deref_open_node(struct kernfs_open_file *of, struct kernfs_node *kn)
bool deref_ok;
deref_ok = (of ? !list_empty(&of->list) : false) ||
- lockdep_is_held(&kernfs_open_file_mutex);
+ lockdep_is_held(kernfs_open_file_mutex_ptr(kn));
on = rcu_dereference_check(kn->attr.open, deref_ok);
@@ -570,19 +586,20 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
struct kernfs_open_file *of)
{
struct kernfs_open_node *on, *new_on = NULL;
+ struct mutex *mutex = NULL;
- mutex_lock(&kernfs_open_file_mutex);
+ mutex = kernfs_open_file_mutex_lock(kn);
on = kernfs_deref_open_node(NULL, kn);
if (on) {
list_add_tail(&of->list, &on->files);
- mutex_unlock(&kernfs_open_file_mutex);
+ mutex_unlock(mutex);
return 0;
} else {
/* not there, initialize a new one */
new_on = kmalloc(sizeof(*new_on), GFP_KERNEL);
if (!new_on) {
- mutex_unlock(&kernfs_open_file_mutex);
+ mutex_unlock(mutex);
return -ENOMEM;
}
atomic_set(&new_on->event, 1);
@@ -591,7 +608,7 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
list_add_tail(&of->list, &new_on->files);
rcu_assign_pointer(kn->attr.open, new_on);
}
- mutex_unlock(&kernfs_open_file_mutex);
+ mutex_unlock(mutex);
return 0;
}
@@ -613,12 +630,13 @@ static void kernfs_unlink_open_file(struct kernfs_node *kn,
struct kernfs_open_file *of)
{
struct kernfs_open_node *on;
+ struct mutex *mutex = NULL;
- mutex_lock(&kernfs_open_file_mutex);
+ mutex = kernfs_open_file_mutex_lock(kn);
on = kernfs_deref_open_node(NULL, kn);
if (!on) {
- mutex_unlock(&kernfs_open_file_mutex);
+ mutex_unlock(mutex);
return;
}
@@ -630,7 +648,7 @@ static void kernfs_unlink_open_file(struct kernfs_node *kn,
kfree_rcu(on, rcu_head);
}
- mutex_unlock(&kernfs_open_file_mutex);
+ mutex_unlock(mutex);
}
static int kernfs_fop_open(struct inode *inode, struct file *file)
@@ -772,7 +790,7 @@ static void kernfs_release_file(struct kernfs_node *kn,
* here because drain path may be called from places which can
* cause circular dependency.
*/
- lockdep_assert_held(&kernfs_open_file_mutex);
+ lockdep_assert_held(kernfs_open_file_mutex_ptr(kn));
if (!of->released) {
/*
@@ -789,11 +807,12 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp)
{
struct kernfs_node *kn = inode->i_private;
struct kernfs_open_file *of = kernfs_of(filp);
+ struct mutex *mutex = NULL;
if (kn->flags & KERNFS_HAS_RELEASE) {
- mutex_lock(&kernfs_open_file_mutex);
+ mutex = kernfs_open_file_mutex_lock(kn);
kernfs_release_file(kn, of);
- mutex_unlock(&kernfs_open_file_mutex);
+ mutex_unlock(mutex);
}
kernfs_unlink_open_file(kn, of);
@@ -808,6 +827,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
{
struct kernfs_open_node *on;
struct kernfs_open_file *of;
+ struct mutex *mutex = NULL;
if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
return;
@@ -823,10 +843,10 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
if (!rcu_access_pointer(kn->attr.open))
return;
- mutex_lock(&kernfs_open_file_mutex);
+ mutex = kernfs_open_file_mutex_lock(kn);
on = kernfs_deref_open_node(NULL, kn);
if (!on) {
- mutex_unlock(&kernfs_open_file_mutex);
+ mutex_unlock(mutex);
return;
}
@@ -840,7 +860,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
kernfs_release_file(kn, of);
}
- mutex_unlock(&kernfs_open_file_mutex);
+ mutex_unlock(mutex);
}
/*
--
2.30.2
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