The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: bdd65589593edd79b6a12ce86b3b7a7c6dae5208 Gitweb: https://git.kernel.org/tip/bdd65589593edd79b6a12ce86b3b7a7c6dae5208 Author: Thomas Gleixner tglx@linutronix.de AuthorDate: Wed, 29 Jul 2020 10:53:28 +02:00 Committer: Ingo Molnar mingo@kernel.org CommitterDate: Wed, 29 Jul 2020 16:27:16 +02:00

x86/i8259: Use printk_deferred() to prevent deadlock

0day reported a possible circular locking dependency:

Chain exists of: &irq_desc_lock_class --> console_owner --> &port_lock_key

Possible unsafe locking scenario:

CPU0 CPU1 ---- ---- lock(&port_lock_key); lock(console_owner); lock(&port_lock_key); lock(&irq_desc_lock_class);

The reason for this is a printk() in the i8259 interrupt chip driver which is invoked with the irq descriptor lock held, which reverses the lock operations vs. printk() from arbitrary contexts.

Switch the printk() to printk_deferred() to avoid that.

Reported-by: kernel test robot lkp@intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Ingo Molnar mingo@kernel.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/87365abt2v.fsf@nanos.tec.linutronix.de --- arch/x86/kernel/i8259.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/i8259.c b/arch/x86/kernel/i8259.c index f3c7625..282b4ee 100644 --- a/arch/x86/kernel/i8259.c +++ b/arch/x86/kernel/i8259.c @@ -207,7 +207,7 @@ spurious_8259A_irq: * lets ACK and report it. [once per IRQ] */ if (!(spurious_irq_mask & irqmask)) { - printk(KERN_DEBUG + printk_deferred(KERN_DEBUG "spurious 8259A interrupt: IRQ%d.\n", irq); spurious_irq_mask |= irqmask; }