wbt_init_enable_default() uses WARN_ON_ONCE to check for failures from wbt_alloc() and wbt_init(). However, both are expected failure paths: - wbt_alloc() can return NULL under memory pressure (-ENOMEM) - wbt_init() can fail with -EBUSY if wbt is already registered syzbot triggers this by injecting memory allocation failures during MTD partition creation via ioctl(BLKPG), causing a spurious warning. wbt_init_enable_default() is a best-effort initialization called from blk_register_queue() with a void return type. Failure simply means the disk operates without writeback throttling, which is harmless. Replace WARN_ON_ONCE with plain if-checks, consistent with how wbt_set_lat() in the same file already handles these failures. Add a pr_warn() for the wbt_init() failure to retain diagnostic information without triggering a full stack trace. Reported-by: syzbot+71fcf20f7c1e5043d78c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=71fcf20f7c1e5043d78c Fixes: 41afaeeda509 ("blk-wbt: fix possible deadlock to nest pcpu_alloc_mutex under q_usage_counter") Signed-off-by: Yuto Ohnuki --- Changes in v2: - Add pr_warn() for wbt_init() failure as suggested by Yu Kuai - Link to v1: https://lore.kernel.org/all/20260315143137.13547-2-ytohnuki@amazon.com/ --- block/blk-wbt.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/block/blk-wbt.c b/block/blk-wbt.c index 33006edfccd4..dcc2438ca16d 100644 --- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -782,10 +782,11 @@ void wbt_init_enable_default(struct gendisk *disk) return; rwb = wbt_alloc(); - if (WARN_ON_ONCE(!rwb)) + if (!rwb) return; - if (WARN_ON_ONCE(wbt_init(disk, rwb))) { + if (wbt_init(disk, rwb)) { + pr_warn("%s: failed to enable wbt\n", disk->disk_name); wbt_free(rwb); return; } -- 2.50.1 Amazon Web Services EMEA SARL, 38 avenue John F. Kennedy, L-1855 Luxembourg, R.C.S. Luxembourg B186284 Amazon Web Services EMEA SARL, Irish Branch, One Burlington Plaza, Burlington Road, Dublin 4, Ireland, branch registration number 908705