2024-05-28 10:30:41

by Tony W Wang-oc

Subject: [PATCH] linux-4.19.y/printk: Avoid logbuf_lock deadlock in oops_end()

A CPU executing vprintk_emit might be interrupted by #PF exception,
this may leads to logbuf_lock deadlock:

CPU x: CPU x:
---- ----
vprintk_emit()
logbuf_lock_irqsave()
printk_safe_enter_irqsave()
A: raw_spin_lock(&logbuf_lock)
vprintk_store() #PF
do_page_fault
...
oops_end
bust_spinlocks(0)
console_unlock()
...
printk_safe_enter_irqsave()
B: raw_spin_lock(&logbuf_lock)

logbuf_lock is taken at A and the deadlock happends at B.

Pass 1 to bust_spinlocks() in the oops_end() to avoid this deadlock.

Signed-off-by: Tony W Wang-oc <[email protected]>
---
arch/x86/kernel/dumpstack.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 7e698c45760c..b4c145ee9536 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -336,7 +336,7 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
if (regs && kexec_should_crash(current))
crash_kexec(regs);

- bust_spinlocks(0);
+ bust_spinlocks(1);
die_owner = -1;
add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
die_nest_count--;
--
2.25.1

2024-05-28 12:47:59

by Greg Kroah-Hartman

Subject: Re: [PATCH] linux-4.19.y/printk: Avoid logbuf_lock deadlock in oops_end()

On Tue, May 28, 2024 at 06:19:57PM +0800, Tony W Wang-oc wrote:
> A CPU executing vprintk_emit might be interrupted by #PF exception,
> this may leads to logbuf_lock deadlock:
>
> CPU x: CPU x:
> ---- ----
> vprintk_emit()
> logbuf_lock_irqsave()
> printk_safe_enter_irqsave()
> A: raw_spin_lock(&logbuf_lock)
> vprintk_store() #PF
> do_page_fault
> ...
> oops_end
> bust_spinlocks(0)
> console_unlock()
> ...
> printk_safe_enter_irqsave()
> B: raw_spin_lock(&logbuf_lock)
>
> logbuf_lock is taken at A and the deadlock happends at B.
>
> Pass 1 to bust_spinlocks() in the oops_end() to avoid this deadlock.
>
> Signed-off-by: Tony W Wang-oc <[email protected]>
> ---
> arch/x86/kernel/dumpstack.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index 7e698c45760c..b4c145ee9536 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -336,7 +336,7 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
> if (regs && kexec_should_crash(current))
> crash_kexec(regs);
>
> - bust_spinlocks(0);
> + bust_spinlocks(1);
> die_owner = -1;
> add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
> die_nest_count--;
> --
> 2.25.1
>

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>