From 0d519bb0de3bf0ac9e6f401d4910fc119062d7be Mon Sep 17 00:00:00 2001 From: Yu Kuai Date: Mon, 30 Jun 2025 19:28:28 +0800 Subject: [PATCH] brd: fix sleeping function called from invalid context in brd_insert_page() __xa_cmpxchg() is called with rcu_read_lock(), and it will allocate memory if necessary. Fix the problem by moving rcu_read_lock() after __xa_cmpxchg(), meanwhile, it still should be held before xa_unlock(), prevent returned page to be freed by concurrent discard. Fixes: bbcacab2e8ee ("brd: avoid extra xarray lookups on first write") Reported-by: syzbot+ea4c8fd177a47338881a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/685ec4c9.a00a0220.129264.000c.GAE@google.com/ Signed-off-by: Yu Kuai Reviewed-by: Christoph Hellwig Link: https://lore.kernel.org/r/20250630112828.421219-1-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe --- drivers/block/brd.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/block/brd.c b/drivers/block/brd.c index b1be6c510372..0c2eabe14af3 100644 --- a/drivers/block/brd.c +++ b/drivers/block/brd.c @@ -64,13 +64,15 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector, rcu_read_unlock(); page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM); - rcu_read_lock(); - if (!page) + if (!page) { + rcu_read_lock(); return ERR_PTR(-ENOMEM); + } xa_lock(&brd->brd_pages); ret = __xa_cmpxchg(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT, NULL, page, gfp); + rcu_read_lock(); if (ret) { xa_unlock(&brd->brd_pages); __free_page(page); -- 2.50.1