On Wed, Aug 13, 2025 at 04:53:10PM +0800, Gu Bowen wrote:
Our syztester report the lockdep WARNING [1]. kmemleak_scan_thread() invokes scan_block() which may invoke a nomal printk() to print warning message. This can cause a deadlock in the scenario reported below:
CPU0 CPU1 ---- ----lock(kmemleak_lock); lock(&port->lock); lock(kmemleak_lock); lock(console_owner);
To solve this problem, switch to printk_safe mode before printing warning message, this will redirect all printk()-s to a special per-CPU buffer, which will be flushed later from a safe context (irq work), and this deadlock problem can be avoided. The proper API to use should be printk_deferred_enter()/printk_deferred_exit() if we want to deferred the printing [2].
This patch also fixes other similar case that need to use the printk deferring [3].
[1] https://lore.kernel.org/all/20250730094914.566582-1-gubowen5@huawei.com/ [2] https://lore.kernel.org/all/5ca375cd-4a20-4807-b897-68b289626550@redhat.com/ [3] https://lore.kernel.org/all/aJCir5Wh362XzLSx@arm.com/ ====================
Cc: stable@vger.kernel.org # 5.10 Signed-off-by: Gu Bowen gubowen5@huawei.com
Reviewed-by: Catalin Marinas catalin.marinas@arm.com