On Wednesday 16 May 2007 22:29, Tim Hockin wrote:
> From: Tim Hockin <[email protected]>
>
> Background:
> The MCE handler has several paths that it can take, depending on various
> conditions of the MCE status and the value of the 'tolerant' knob. The
> exact semantics are not well defined and the code is a bit twisty.
>
> Description:
> This patch makes the MCE handler's behavior more clear by documenting the
> behavior for various 'tolerant' levels. It also fixes or enhances
> several small things in the handler. Specifically:
> * If RIPV is set it is not safe to restart, so set the 'no way out'
> flag rather than the 'kill it' flag.
Why? It is not PCC. We cannot return of course, but killing isn't returning.
> * Don't panic() on correctable MCEs.
The idea behind this was that if you get an exception it is always a bit risky
because there are a few potential deadlocks that cannot be avoided.
And normally non UC is just polled which will never cause a panic.
So I don't quite see the value of this change.
> This patch also calls nonseekable_open() in mce_open (as suggested by akpm).
That should be a separate patch
> + 0: always panic on uncorrected errors, log corrected errors
> + 1: panic or SIGBUS on uncorrected errors, log corrected errors
> + 2: SIGBUS or log uncorrected errors, log corrected errors
Just saying SIGBUS is misleading because it isn't a catchable
signal.
> +
> + /*
> + * If the error seems to be unrecoverable, something should be
> + * done. Try to kill as little as possible. If we can kill just
> + * one task, do that. If the user has set the tolerance very
> + * high, don't try to do anything at all.
> + */
> + if (kill_it && tolerant < 3) {
> int user_space = 0;
>
> - if (m.mcgstatus & MCG_STATUS_RIPV)
> + /*
> + * If the EIPV bit is set, it means the saved IP is the
> + * instruction which caused the MCE.
> + */
> + if (m.mcgstatus & MCG_STATUS_EIPV)
> user_space = panicm.rip && (panicm.cs & 3);
> -
> - /* When the machine was in user space and the CPU didn't get
> - confused it's normally not necessary to panic, unless you
> - are paranoid (tolerant == 0)
> -
> - RED-PEN could be more tolerant for MCEs in idle,
> - but most likely they occur at boot anyways, where
> - it is best to just halt the machine. */
> - if ((!user_space && (panic_on_oops || tolerant < 2)) ||
> - (unsigned)current->pid <= 1)
> - mce_panic("Uncorrected machine check", &panicm, mcestart);
> -
> - /* do_exit takes an awful lot of locks and has as
> - slight risk of deadlocking. If you don't want that
> - don't set tolerant >= 2 */
> - if (tolerant < 3)
> +
> + /*
> + * If we know that the error was in user space, send a
> + * SIGBUS. Otherwise, panic if tolerance is low.
> + *
> + * do_exit() takes an awful lot of locks and has a slight
> + * risk of deadlocking.
> + */
> + if (user_space) {
> do_exit(SIGBUS);
> + } else if (panic_on_oops || tolerant < 2) {
> + mce_panic("Uncorrected machine check",
> + &panicm, mcestart);
> + }
Why did you remove the idle special case?
-Andi
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