Patch "libfs: Re-arrange locking in offset_iterate_dir()" has been added to the 6.6-stable tree

Commit Message

Greg Kroah-Hartman Jan. 30, 2025, 8:59 a.m. UTC

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This is a note to let you know that I've just added the patch titled

    libfs: Re-arrange locking in offset_iterate_dir()

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     libfs-re-arrange-locking-in-offset_iterate_dir.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <[e-mail]> know about it.


From stable+bounces-110401-greg=[e-mail] Fri Jan 24 20:20:29 2025
From: [e-mail]
Date: Fri, 24 Jan 2025 14:19:36 -0500
Subject: libfs: Re-arrange locking in offset_iterate_dir()
To: Hugh Dickins <[e-mail]>, Andrew Morten <[e-mail]>, Christian Brauner <[e-mail]>, Al Viro <[e-mail]>, Greg Kroah-Hartman <[e-mail]>, Sasha Levin <[e-mail]>
Cc: <[e-mail]>, <[e-mail]>, <[e-mail]>, [e-mail], [e-mail], Chuck Lever <[e-mail]>, "Liam R. Howlett" <[e-mail]>, Jan Kara <[e-mail]>
Message-ID: <[e-mail]>

From: Chuck Lever <[e-mail]>

[ Upstream commit 3f6d810665dfde0d33785420618ceb03fba0619d ]

Liam and Matthew say that once the RCU read lock is released,
xa_state is not safe to re-use for the next xas_find() call. But the
RCU read lock must be released on each loop iteration so that
dput(), which might_sleep(), can be called safely.

Thus we are forced to walk the offset tree with fresh state for each
directory entry. xa_find() can do this for us, though it might be a
little less efficient than maintaining xa_state locally.

We believe that in the current code base, inode->i_rwsem provides
protection for the xa_state maintained in
offset_iterate_dir(). However, there is no guarantee that will
continue to be the case in the future.

Since offset_iterate_dir() doesn't build xa_state locally any more,
there's no longer a strong need for offset_find_next(). Clean up by
rolling these two helpers together.

Suggested-by: Liam R. Howlett <[e-mail]>
Message-ID: <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Jan Kara <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>
---
 fs/libfs.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)



Patches currently in stable-queue which might be from [e-mail] are

queue-6.6/libfs-replace-simple_offset-end-of-directory-detection.patch
queue-6.6/libfs-re-arrange-locking-in-offset_iterate_dir.patch
queue-6.6/libfs-add-simple_offset_empty.patch
queue-6.6/shmem-fix-shmem_rename2.patch
queue-6.6/revert-libfs-add-simple_offset_empty.patch
queue-6.6/libfs-use-d_children-list-to-iterate-simple_offset-directories.patch
queue-6.6/libfs-define-a-minimum-directory-offset.patch
queue-6.6/libfs-return-enospc-when-the-directory-offset-range-is-exhausted.patch
queue-6.6/libfs-fix-simple_offset_rename_exchange.patch
queue-6.6/libfs-add-simple_offset_rename-api.patch

Patch

--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -401,12 +401,13 @@  static loff_t offset_dir_llseek(struct f
 	return vfs_setpos(file, offset, U32_MAX);
 }
 
-static struct dentry *offset_find_next(struct xa_state *xas)
+static struct dentry *offset_find_next(struct offset_ctx *octx, loff_t offset)
 {
 	struct dentry *child, *found = NULL;
+	XA_STATE(xas, &octx->xa, offset);
 
 	rcu_read_lock();
-	child = xas_next_entry(xas, U32_MAX);
+	child = xas_next_entry(&xas, U32_MAX);
 	if (!child)
 		goto out;
 	spin_lock(&child->d_lock);
@@ -429,12 +430,11 @@  static bool offset_dir_emit(struct dir_c
 
 static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
 {
-	struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode);
-	XA_STATE(xas, &so_ctx->xa, ctx->pos);
+	struct offset_ctx *octx = inode->i_op->get_offset_ctx(inode);
 	struct dentry *dentry;
 
 	while (true) {
-		dentry = offset_find_next(&xas);
+		dentry = offset_find_next(octx, ctx->pos);
 		if (!dentry)
 			return ERR_PTR(-ENOENT);
 
@@ -443,8 +443,8 @@  static void *offset_iterate_dir(struct i
 			break;
 		}
 
+		ctx->pos = dentry2offset(dentry) + 1;
 		dput(dentry);
-		ctx->pos = xas.xa_index + 1;
 	}
 	return NULL;
 }