Re: [PATCH printk v3 4/7] printk: Do not take console lock for console_flush_on_panic()

[Sergey Senozhatsky]

On (23/07/17 21:52), John Ogness wrote:
> 
> Currently console_flush_on_panic() will attempt to acquire the
> console lock when flushing the buffer on panic. If it fails to
> acquire the lock, it continues anyway because this is the last
> chance to get any pending records printed.
> 
> The reason why the console lock was attempted at all was to
> prevent any other CPUs from acquiring the console lock for
> printing while the panic CPU was printing. But as of the
> previous commit, non-panic CPUs will no longer attempt to
> acquire the console lock in a panic situation. Therefore it is
> no longer strictly necessary for a panic CPU to acquire the
> console lock.
> 
> Avoiding taking the console lock when flushing in panic has
> the additional benefit of avoiding possible deadlocks due to
> semaphore usage in NMI context (semaphores are not NMI-safe)
> and avoiding possible deadlocks if another CPU accesses the
> semaphore and is stopped while holding one of the semaphore's
> internal spinlocks.
> 
> Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>

Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>