[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <d40a41e428c07f88ea011fbf191bd8efac94c523.1756222465.git.josef@toxicpanda.com>
Date: Tue, 26 Aug 2025 11:39:23 -0400
From: Josef Bacik <josef@...icpanda.com>
To: linux-fsdevel@...r.kernel.org,
linux-btrfs@...r.kernel.org,
kernel-team@...com,
linux-ext4@...r.kernel.org,
linux-xfs@...r.kernel.org,
brauner@...nel.org,
viro@...IV.linux.org.uk,
amir73il@...il.com
Subject: [PATCH v2 23/54] fs: use refcount_inc_not_zero in igrab
We are going to use igrab everywhere we want to acquire a live inode.
Update it to do a refcount_inc_not_zero on the i_count, and if
successful grab an reference to i_obj_count. Add a comment explaining
why we do this and the safety.
Signed-off-by: Josef Bacik <josef@...icpanda.com>
---
fs/inode.c | 26 +++++++++++++-------------
include/linux/fs.h | 30 ++++++++++++++++++++++++++++++
2 files changed, 43 insertions(+), 13 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index 0be1c137bf1e..66402786cf8f 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1632,20 +1632,20 @@ EXPORT_SYMBOL(iunique);
struct inode *igrab(struct inode *inode)
{
+ lockdep_assert_not_held(&inode->i_lock);
+
+ inode = inode_tryget(inode);
+ if (!inode)
+ return NULL;
+
+ /*
+ * If this inode is on the LRU, take it off so that we can re-run the
+ * LRU logic on the next iput().
+ */
spin_lock(&inode->i_lock);
- if (!(inode->i_state & (I_FREEING|I_WILL_FREE))) {
- __iget(inode);
- inode_lru_list_del(inode);
- spin_unlock(&inode->i_lock);
- } else {
- spin_unlock(&inode->i_lock);
- /*
- * Handle the case where s_op->clear_inode is not been
- * called yet, and somebody is calling igrab
- * while the inode is getting freed.
- */
- inode = NULL;
- }
+ inode_lru_list_del(inode);
+ spin_unlock(&inode->i_lock);
+
return inode;
}
EXPORT_SYMBOL(igrab);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index fc23e37ca250..b13d057ad0d7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3393,6 +3393,36 @@ static inline unsigned int iobj_count_read(const struct inode *inode)
return refcount_read(&inode->i_obj_count);
}
+static inline struct inode *inode_tryget(struct inode *inode)
+{
+ /*
+ * We are using inode_tryget() because we're interested in getting a
+ * live reference to the inode, which is ->i_count. Normally we would
+ * grab i_obj_count first, as it is the higher priority reference.
+ * However we're only interested in making sure we have a live inode,
+ * and we know that if we get a reference for i_count then we can safely
+ * acquire i_obj_count because we always drop i_obj_count after dropping
+ * an i_count reference.
+ *
+ * This is meant to be used either in a place where we have an existing
+ * i_obj_count reference on the inode, or under rcu_read_lock() so we
+ * know we're safe in accessing this inode still.
+ */
+ VFS_WARN_ON_ONCE(!iobj_count_read(inode) && !rcu_read_lock_held());
+
+ if (refcount_inc_not_zero(&inode->i_count)) {
+ iobj_get(inode);
+ return inode;
+ }
+
+ /*
+ * If we failed to increment the reference count, then the
+ * inode is being freed or has been freed. We return NULL
+ * in this case.
+ */
+ return NULL;
+}
+
/*
* inode->i_lock must be held
*/
--
2.49.0
Powered by blists - more mailing lists