Messages in this thread | | | From | Sergey Senozhatsky <> | Date | Sat, 13 Jul 2019 22:19:47 +0900 | Subject | Re: [PATCH] kernel/printk: prevent deadlock at calling kmsg_dump from NMI context |
| |
On (07/13/19 09:46), Konstantin Khlebnikov wrote: > > On (07/12/19 17:54), Konstantin Khlebnikov wrote: > > Yep printk() can deal with NMI, but kmsg_dump() is a different beast. > It reads printk buffer and saves content into persistent storage like ACPI ERST.
Ah, sorry! I misread your patch. Yeah, I see what you are doing.
OK. So, I guess that for kmsg_dump(KMSG_DUMP_PANIC) we should be fine in general.
We call kmsg_dump(KMSG_DUMP_PANIC) after smp_send_stop() and after printk_safe_flush_on_panic(). printk_safe_flush_on_panic() resets the state of logbuf_lock, so logbuf_lock, in general case, should be unlocked by the time we call kmsg_dump(KMSG_DUMP_PANIC). Even for nested contexts.
CPU0 printk() logbuf_lock_irqsave(flags) -> NMI panic() smp_send_stop() printk_safe_flush_on_panic() raw_spin_lock_init(&logbuf_lock) << reinit >> kmsg_dump(KMSG_DUMP_PANIC) logbuf_lock_irqsave(flags) << expected to be OK >>
So do we have strong reasons to disable NMI->panic->kmsg_dump(DUMP_PANIC)?
Other kmsg_dump(), maybe, can experience some troubles sometimes, need to check that.
-ss
| |