From: Oleg Nesterov <oleg@redhat.com>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Namhyung Kim <namhyung@kernel.org>,
David Ahern <dsahern@gmail.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Milind Chabbi <chabbi.milind@gmail.com>,
Frederic Weisbecker <frederic@kernel.org>
Subject: Re: [PATCH 4/5] perf/hw_breakpoint: Set breakpoint as disabled in modify_user_hw_breakpoint error path
Date: Thu, 9 Aug 2018 16:17:13 +0200 [thread overview]
Message-ID: <20180809141713.GB22636@redhat.com> (raw)
In-Reply-To: <20180809120305.20693-5-jolsa@kernel.org>
On 08/09, Jiri Olsa wrote:
>
> @@ -523,8 +523,10 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
> perf_event_disable(bp);
>
> err = modify_user_hw_breakpoint_check(bp, attr, false);
> - if (err)
> + if (err) {
> + bp->attr.disabled = 1;
> return err;
Yes, but on the second thought... Can't we simply do
int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
{
int err;
/*
* modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
* will not be possible to raise IPIs that invoke __perf_event_disable.
* So call the function directly after making sure we are targeting the
* current task.
*/
if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
perf_event_disable_local(bp);
else
perf_event_disable(bp);
err = modify_user_hw_breakpoint_check(bp, attr, false);
if (!bp.attr->disabled)
perf_event_enable(bp);
return err;
}
instead of this and the next patch?
We can do this because (as you pointed out) validate_hw_breakpoint() has already
gone in -tip tree, and (afaics) modify_user_hw_breakpoint_check() never changes
perf_event's state on failure, so we can safely "restart" this bp if it was enabled
before.
1. This is what we had before the recent f67b15037a7a50c57f72e69a6d59941ad90a0f0f
"perf/hwbp: Simplify the perf-hwbp code, fix documentation".
Note that this commit was actually the bug fix which introduced another problem
fixed by your 2/5.
But see above, perf_event_enable() is no longer unsafe after
modify_user_hw_breakpoint_check(), we can restore the previous semantics.
2. This matches perf_event_modify_breakpoint(). Which btw can be simplified a bit,
it too can simply do
if (!bp->attr.disabled)
_perf_event_enable(bp);
return err;
Oleg.
next prev parent reply other threads:[~2018-08-09 14:17 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-09 12:03 [PATCHv2 0/5] perf/hw_breakpoint: Fix breakpoint modify Jiri Olsa
2018-08-09 12:03 ` [PATCH 1/5] perf tests: Add breakpoint modify tests Jiri Olsa
2018-08-09 12:03 ` [PATCH 2/5] perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set Jiri Olsa
2018-08-09 12:03 ` [PATCH 3/5] perf/hw_breakpoint: Remove superfluous bp->attr.disabled = 0 Jiri Olsa
2018-08-09 13:59 ` Oleg Nesterov
2018-08-09 12:03 ` [PATCH 4/5] perf/hw_breakpoint: Set breakpoint as disabled in modify_user_hw_breakpoint error path Jiri Olsa
2018-08-09 14:17 ` Oleg Nesterov [this message]
2018-08-09 16:30 ` Jiri Olsa
2018-08-28 14:29 ` Arnaldo Carvalho de Melo
2018-08-28 14:38 ` Jiri Olsa
2018-08-28 14:39 ` Arnaldo Carvalho de Melo
2018-08-09 12:03 ` [PATCH 5/5] perf/hw_breakpoint: Add fallback code for ptrace_set_breakpoint_addr Jiri Olsa
2018-08-28 14:25 ` [PATCHv2 0/5] perf/hw_breakpoint: Fix breakpoint modify Arnaldo Carvalho de Melo
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