Messages in this thread | | | Date | Thu, 1 Jun 2023 13:48:06 +0900 | From | Masami Hiramatsu (Google) <> | Subject | Re: [PATCH v2] x86/alternatives: Add cond_resched() to text_poke_bp_batch() |
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On Wed, 31 May 2023 09:24:19 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org> > > Debugging in the kernel has started slowing down the kernel by a > noticeable amount. The ftrace start up tests are triggering the softlockup > watchdog on some boxes. This is caused by the start up tests that enable > function and function graph tracing several times. Sprinkling > cond_resched() just in the start up test code was not enough to stop the > softlockup from triggering. It would sometimes trigger in the > text_poke_bp_batch() code. > > When function tracing enables all functions, it will call > text_poke_queue() to queue the places that need to be patched. Every > 256 entries will do a "flush" that calls text_poke_bp_batch() to do the > update of the 256 locations. As this is in a scheduleable context, > calling cond_resched() at the start of text_poke_bp_batch() will ensure > that other tasks could get a chance to run while the patching is > happening. This keeps the softlockup from triggering in the start up > tests. >
Looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Thank you!
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> > --- > Changes since v1: https://lkml.kernel.org/r/20230528084652.5f3b48f0@rorschach.local.home > > - Just call cond_resched() once in text_poke_bp_batch() and not for > each phase, as it only needs to be called once every 256 entries. > > arch/x86/kernel/alternative.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index f615e0cb6d93..412ad66cd240 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -1953,6 +1953,16 @@ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries > */ > atomic_set_release(&bp_desc.refs, 1); > > + /* > + * Function tracing can enable thousands of places that need to be > + * updated. This can take quite some time, and with full kernel debugging > + * enabled, this could cause the softlockup watchdog to trigger. > + * This function gets called every 256 entries added to be patched. > + * Call cond_resched() here to make sure that other tasks can get scheduled > + * while processing all the functions being patched. > + */ > + cond_resched(); > + > /* > * Corresponding read barrier in int3 notifier for making sure the > * nr_entries and handler are correctly ordered wrt. patching. > -- > 2.39.2 >
-- Masami Hiramatsu (Google) <mhiramat@kernel.org>
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