linux-kernel - [PATCH v2] btrfs: fix comment in alloc

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Message-ID: <20251003133001.45052-2-rtapadia730@gmail.com>
Date: Fri,  3 Oct 2025 19:00:02 +0530
From: rtapadia730@...il.com
To: dsterba@...e.com,
	clm@...com,
	fdmanana@...nel.org
Cc: linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	khalid@...nel.org,
	david.hunter.linux@...il.com,
	Rajeev Tapadia <rtapadia730@...il.com>
Subject: [PATCH v2] btrfs: fix comment in alloc_bitmap() and drop stale TODO

From: Rajeev Tapadia <rtapadia730@...il.com>

All callers of alloc_bitmap() hold a transaction handle, so GFP_NOFS is
needed to avoid deadlocks on recursion. Update the comment and drop the
stale TODO.

Signed-off-by: Rajeev Tapadia <rtapadia730@...il.com>
---
Change log:
As per previous review the change is not required. So just removing the
stale TODO.

 fs/btrfs/free-space-tree.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
index dad0b492a663..bb8ca7b679be 100644
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -165,11 +165,9 @@ static unsigned long *alloc_bitmap(u32 bitmap_size)
 
 	/*
 	 * GFP_NOFS doesn't work with kvmalloc(), but we really can't recurse
-	 * into the filesystem as the free space bitmap can be modified in the
-	 * critical section of a transaction commit.
-	 *
-	 * TODO: push the memalloc_nofs_{save,restore}() to the caller where we
-	 * know that recursion is unsafe.
+	 * into the filesystem here. All callers hold a transaction handle
+	 * open, so if a GFP_KERNEL allocation recurses into the filesystem
+	 * and triggers a transaction commit, we would deadlock.
 	 */
 	nofs_flag = memalloc_nofs_save();
 	ret = kvzalloc(bitmap_rounded_size, GFP_KERNEL);
-- 
2.51.0