linux-kernel - [PATCH] brd: fix sleeping memory allocation in brd_insert

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Message-ID: <11cb9a09-f66c-4c46-bd38-fc6080413c29@I-love.SAKURA.ne.jp>
Date: Sat, 28 Jun 2025 17:36:00 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Jens Axboe <axboe@...nel.dk>, Yu Kuai <yukuai3@...wei.com>,
        Christoph Hellwig <hch@....de>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] brd: fix sleeping memory allocation in brd_insert_page()

syzbot is reporting that brd_insert_page() is calling
__xa_cmpxchg(__GFP_DIRECT_RECLAIM) with spinlock and RCU lock held.
Change __xa_cmpxchg() to use GFP_NOWAIT | __GFP_NOWARN, for it is likely
that __xa_cmpxchg() succeeds because of preceding alloc_page().

Fixes: bbcacab2e8ee ("brd: avoid extra xarray lookups on first write")
Reported-by: syzbot+ea4c8fd177a47338881a@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ea4c8fd177a47338881a
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
 drivers/block/brd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index b1be6c510372..ed3eb931750c 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -70,7 +70,7 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector,
 
 	xa_lock(&brd->brd_pages);
 	ret = __xa_cmpxchg(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT, NULL,
-			page, gfp);
+			page, GFP_NOWAIT | __GFP_NOWARN);
 	if (ret) {
 		xa_unlock(&brd->brd_pages);
 		__free_page(page);
-- 
2.50.0