From: Ian Rogers <irogers@google.com>
To: Marco Elver <elver@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <frederic@kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Dmitry Vyukov <dvyukov@google.com>,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev@lists.ozlabs.org, linux-perf-users@vger.kernel.org,
x86@kernel.org, linux-sh@vger.kernel.org,
kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 09/14] powerpc/hw_breakpoint: Avoid relying on caller synchronization
Date: Wed, 20 Jul 2022 08:35:20 -0700 [thread overview]
Message-ID: <CAP-5=fXevVEC9MFuArG7nLadwEDzzWRLeBBkCUqDdJz9X=Bvjg@mail.gmail.com> (raw)
In-Reply-To: <20220704150514.48816-10-elver@google.com>
On Mon, Jul 4, 2022 at 8:07 AM Marco Elver <elver@google.com> wrote:
>
> Internal data structures (cpu_bps, task_bps) of powerpc's hw_breakpoint
> implementation have relied on nr_bp_mutex serializing access to them.
>
> Before overhauling synchronization of kernel/events/hw_breakpoint.c,
> introduce 2 spinlocks to synchronize cpu_bps and task_bps respectively,
> thus avoiding reliance on callers synchronizing powerpc's hw_breakpoint.
>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Marco Elver <elver@google.com>
> Acked-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Ian Rogers <irogers@google.com>
Thanks,
Ian
> ---
> v2:
> * New patch.
> ---
> arch/powerpc/kernel/hw_breakpoint.c | 53 ++++++++++++++++++++++-------
> 1 file changed, 40 insertions(+), 13 deletions(-)
>
> diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
> index 2669f80b3a49..8db1a15d7acb 100644
> --- a/arch/powerpc/kernel/hw_breakpoint.c
> +++ b/arch/powerpc/kernel/hw_breakpoint.c
> @@ -15,6 +15,7 @@
> #include <linux/kernel.h>
> #include <linux/sched.h>
> #include <linux/smp.h>
> +#include <linux/spinlock.h>
> #include <linux/debugfs.h>
> #include <linux/init.h>
>
> @@ -129,7 +130,14 @@ struct breakpoint {
> bool ptrace_bp;
> };
>
> +/*
> + * While kernel/events/hw_breakpoint.c does its own synchronization, we cannot
> + * rely on it safely synchronizing internals here; however, we can rely on it
> + * not requesting more breakpoints than available.
> + */
> +static DEFINE_SPINLOCK(cpu_bps_lock);
> static DEFINE_PER_CPU(struct breakpoint *, cpu_bps[HBP_NUM_MAX]);
> +static DEFINE_SPINLOCK(task_bps_lock);
> static LIST_HEAD(task_bps);
>
> static struct breakpoint *alloc_breakpoint(struct perf_event *bp)
> @@ -174,7 +182,9 @@ static int task_bps_add(struct perf_event *bp)
> if (IS_ERR(tmp))
> return PTR_ERR(tmp);
>
> + spin_lock(&task_bps_lock);
> list_add(&tmp->list, &task_bps);
> + spin_unlock(&task_bps_lock);
> return 0;
> }
>
> @@ -182,6 +192,7 @@ static void task_bps_remove(struct perf_event *bp)
> {
> struct list_head *pos, *q;
>
> + spin_lock(&task_bps_lock);
> list_for_each_safe(pos, q, &task_bps) {
> struct breakpoint *tmp = list_entry(pos, struct breakpoint, list);
>
> @@ -191,6 +202,7 @@ static void task_bps_remove(struct perf_event *bp)
> break;
> }
> }
> + spin_unlock(&task_bps_lock);
> }
>
> /*
> @@ -200,12 +212,17 @@ static void task_bps_remove(struct perf_event *bp)
> static bool all_task_bps_check(struct perf_event *bp)
> {
> struct breakpoint *tmp;
> + bool ret = false;
>
> + spin_lock(&task_bps_lock);
> list_for_each_entry(tmp, &task_bps, list) {
> - if (!can_co_exist(tmp, bp))
> - return true;
> + if (!can_co_exist(tmp, bp)) {
> + ret = true;
> + break;
> + }
> }
> - return false;
> + spin_unlock(&task_bps_lock);
> + return ret;
> }
>
> /*
> @@ -215,13 +232,18 @@ static bool all_task_bps_check(struct perf_event *bp)
> static bool same_task_bps_check(struct perf_event *bp)
> {
> struct breakpoint *tmp;
> + bool ret = false;
>
> + spin_lock(&task_bps_lock);
> list_for_each_entry(tmp, &task_bps, list) {
> if (tmp->bp->hw.target == bp->hw.target &&
> - !can_co_exist(tmp, bp))
> - return true;
> + !can_co_exist(tmp, bp)) {
> + ret = true;
> + break;
> + }
> }
> - return false;
> + spin_unlock(&task_bps_lock);
> + return ret;
> }
>
> static int cpu_bps_add(struct perf_event *bp)
> @@ -234,6 +256,7 @@ static int cpu_bps_add(struct perf_event *bp)
> if (IS_ERR(tmp))
> return PTR_ERR(tmp);
>
> + spin_lock(&cpu_bps_lock);
> cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu);
> for (i = 0; i < nr_wp_slots(); i++) {
> if (!cpu_bp[i]) {
> @@ -241,6 +264,7 @@ static int cpu_bps_add(struct perf_event *bp)
> break;
> }
> }
> + spin_unlock(&cpu_bps_lock);
> return 0;
> }
>
> @@ -249,6 +273,7 @@ static void cpu_bps_remove(struct perf_event *bp)
> struct breakpoint **cpu_bp;
> int i = 0;
>
> + spin_lock(&cpu_bps_lock);
> cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu);
> for (i = 0; i < nr_wp_slots(); i++) {
> if (!cpu_bp[i])
> @@ -260,19 +285,25 @@ static void cpu_bps_remove(struct perf_event *bp)
> break;
> }
> }
> + spin_unlock(&cpu_bps_lock);
> }
>
> static bool cpu_bps_check(int cpu, struct perf_event *bp)
> {
> struct breakpoint **cpu_bp;
> + bool ret = false;
> int i;
>
> + spin_lock(&cpu_bps_lock);
> cpu_bp = per_cpu_ptr(cpu_bps, cpu);
> for (i = 0; i < nr_wp_slots(); i++) {
> - if (cpu_bp[i] && !can_co_exist(cpu_bp[i], bp))
> - return true;
> + if (cpu_bp[i] && !can_co_exist(cpu_bp[i], bp)) {
> + ret = true;
> + break;
> + }
> }
> - return false;
> + spin_unlock(&cpu_bps_lock);
> + return ret;
> }
>
> static bool all_cpu_bps_check(struct perf_event *bp)
> @@ -286,10 +317,6 @@ static bool all_cpu_bps_check(struct perf_event *bp)
> return false;
> }
>
> -/*
> - * We don't use any locks to serialize accesses to cpu_bps or task_bps
> - * because are already inside nr_bp_mutex.
> - */
> int arch_reserve_bp_slot(struct perf_event *bp)
> {
> int ret;
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>
next prev parent reply other threads:[~2022-07-20 15:35 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-04 15:05 [PATCH v3 00/14] perf/hw_breakpoint: Optimize for thousands of tasks Marco Elver
2022-07-04 15:05 ` [PATCH v3 01/14] perf/hw_breakpoint: Add KUnit test for constraints accounting Marco Elver
2022-07-04 15:10 ` Dmitry Vyukov
2022-07-20 15:22 ` Ian Rogers
2022-07-21 16:22 ` Mark Rutland
2022-07-22 9:10 ` Will Deacon
2022-07-22 9:20 ` Dmitry Vyukov
2022-07-22 10:10 ` Will Deacon
2022-07-22 10:31 ` Dmitry Vyukov
2022-07-22 11:03 ` Will Deacon
2022-07-22 13:41 ` Dmitry Vyukov
2022-07-25 11:00 ` Marco Elver
2022-07-04 15:05 ` [PATCH v3 02/14] perf/hw_breakpoint: Provide hw_breakpoint_is_used() and use in test Marco Elver
2022-07-04 15:09 ` Dmitry Vyukov
2022-07-20 15:22 ` Ian Rogers
2022-07-04 15:05 ` [PATCH v3 03/14] perf/hw_breakpoint: Clean up headers Marco Elver
2022-07-20 15:23 ` Ian Rogers
2022-07-04 15:05 ` [PATCH v3 04/14] perf/hw_breakpoint: Optimize list of per-task breakpoints Marco Elver
2022-07-20 15:29 ` Ian Rogers
2022-07-20 15:39 ` Marco Elver
2022-07-04 15:05 ` [PATCH v3 05/14] perf/hw_breakpoint: Mark data __ro_after_init Marco Elver
2022-07-20 15:30 ` Ian Rogers
2022-07-04 15:05 ` [PATCH v3 06/14] perf/hw_breakpoint: Optimize constant number of breakpoint slots Marco Elver
2022-07-20 15:31 ` Ian Rogers
2022-07-04 15:05 ` [PATCH v3 07/14] perf/hw_breakpoint: Make hw_breakpoint_weight() inlinable Marco Elver
2022-07-20 15:32 ` Ian Rogers
2022-07-04 15:05 ` [PATCH v3 08/14] perf/hw_breakpoint: Remove useless code related to flexible breakpoints Marco Elver
2022-07-20 15:34 ` Ian Rogers
2022-07-04 15:05 ` [PATCH v3 09/14] powerpc/hw_breakpoint: Avoid relying on caller synchronization Marco Elver
2022-07-20 15:35 ` Ian Rogers [this message]
2022-07-04 15:05 ` [PATCH v3 10/14] locking/percpu-rwsem: Add percpu_is_write_locked() and percpu_is_read_locked() Marco Elver
2022-07-20 15:36 ` Ian Rogers
2022-08-17 12:47 ` Peter Zijlstra
2022-08-29 6:00 ` Marco Elver
2022-07-04 15:05 ` [PATCH v3 11/14] perf/hw_breakpoint: Reduce contention with large number of tasks Marco Elver
2022-07-20 15:38 ` Ian Rogers
2022-08-17 13:03 ` Peter Zijlstra
2022-08-17 13:14 ` Marco Elver
2022-08-29 8:38 ` Peter Zijlstra
2022-08-29 9:38 ` Marco Elver
2022-07-04 15:05 ` [PATCH v3 12/14] perf/hw_breakpoint: Introduce bp_slots_histogram Marco Elver
2022-07-20 15:40 ` Ian Rogers
2022-07-04 15:05 ` [PATCH v3 13/14] perf/hw_breakpoint: Optimize max_bp_pinned_slots() for CPU-independent task targets Marco Elver
2022-07-20 15:42 ` Ian Rogers
2022-07-04 15:05 ` [PATCH v3 14/14] perf/hw_breakpoint: Optimize toggle_bp_slot() " Marco Elver
2022-07-20 15:44 ` Ian Rogers
2022-07-12 13:39 ` [PATCH v3 00/14] perf/hw_breakpoint: Optimize for thousands of tasks Marco Elver
2022-07-20 15:47 ` Ian Rogers
2022-08-16 14:12 ` Marco Elver
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