Messages in this thread | | | From | John Ogness <> | Subject | Re: [PATCH printk v1 02/18] printk: Add NMI check to down_trylock_console_sem() | Date | Fri, 17 Mar 2023 12:43:56 +0106 |
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On 2023-03-07, Petr Mladek <pmladek@suse.com> wrote: > So that this change would cause a non-paired console_unlock(). > And console_unlock might still deadlock on the console_sem->lock.
Yes, but at least it would have flushed beforehand.
> One solution would be to call console_flush_all() directly in > console_flush_on_panic() without taking console_lock(). > > It should not be worse than the current code which ignores > the console_trylock() return value.
I think your suggestion is acceptable.
> Note that it mostly works because console_flush_on_panic() is called > when other CPUs are supposed to be stopped. > > We only would need to prevent other CPUs from flushing messages > as well if they were still running by chance. But we actually already > do this, see abandon_console_lock_in_panic(). Well, we should > make sure that the abandon_console_lock_in_panic() check is > done before flushing the first message. > > All these changes together would prevent deadlock on > console_sem->lock. But the synchronization "guarantees" should stay > the same.
We could also update console_trylock() and console_lock() to fail and infinitely sleep, respectively, when abandon_console_lock_in_panic() is true. That would prevent CPUs from newly acquiring the console lock and interfering with the panic CPU.
John
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