Messages in this thread | | | Date | Thu, 1 Sep 2022 14:46:48 -0300 | Subject | Re: [PATCH V3] firmware: google: Test spinlock on panic path to avoid lockups | From | "Guilherme G. Piccoli" <> |
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On 01/09/2022 13:44, Greg KH wrote: > [...] >>> How are we supposed to know this here? >>> >> >> Reading the code? >> Or you mean, in the commit description this should be mentioned? > > Yes, and in the comment as this type of call is very rare and should > almost never be used.
OK, I can add that, for sure.
>> [...] >> I don't think it is so simple - we are in the panic path. > > Great, then the lock doesn't matter :) > >> So, imagine the lock was taken in CPU0, where GSMI is doing some >> operation. During that operation, CPU1 panics! >> >> When that happens, panic() executes in CPU1, disabling CPU0 through >> "strong" mechanisms (NMI). So, CPU0 had the lock, it is now off, and >> when CPU1 goes through the panic notifiers, it'll eventually wait >> forever for this lock in the GSMI handler, unless we have this patch >> that would prevent the handler to run in such case. >> Makes sense? > > I'm trying to say "if you are in panic, never grab the lock in the first > place". So change the place when you grab the lock, not here. >
Evan, any comment here? I think the patch is still well suited for this case. Suggestions on how to improve it are welcome, of course.
I honestly didn't understand exactly what you're suggesting Greg... Mind clarifying?
Cheers,
Guilherme
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