Messages in this thread | | | Date | Wed, 26 Jan 2022 19:06:44 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH 2/4] printk: disable optimistic spin during panic |
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On (22/01/26 10:51), John Ogness wrote: > > Is there something that prevents panic CPU from NMI hlt CPU which is > > in console_trylock() under raw_spin_lock_irqsave()? > > > > CPU0 CPU1 > > console_trylock_spinnning() > > console_trylock() > > down_trylock() > > raw_spin_lock_irqsave(&sem->lock) > > > > panic() > > crash_smp_send_stop() > > NMI -> HALT > > This is a good point. I wonder if console_flush_on_panic() should > perform a sema_init() before it does console_trylock().
A long time ago there was zap_locks() function in printk, that used to re-init console semaphore and logbuf spin_lock, but _only_ in case of printk recursion (which was never reliable)
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/kernel/printk/printk.c?h=v4.9.297#n1557
This has been superseded by printk_safe per-CPU buffers so we removed that function.
So it could be that may be we want to introduce something similar to zap_locks() again.
All reasonable serial consoles drivers should take oops_in_progress into consideration in ->write(), so we probably don't care for console_drivers spinlocks, etc. but potentially can do a bit better on the printk side.
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