Commit-ID: 8a58ddae23796c733c5dfbd717538d89d036c5bd Gitweb: https://git.kernel.org/tip/8a58ddae23796c733c5dfbd717538d89d036c5bd Author: Alexander Shishkin alexander.shishkin@linux.intel.com AuthorDate: Mon, 1 Jul 2019 14:07:55 +0300 Committer: Ingo Molnar mingo@kernel.org CommitDate: Sat, 13 Jul 2019 11:21:28 +0200

perf/core: Fix exclusive events' grouping

So far, we tried to disallow grouping exclusive events for the fear of complications they would cause with moving between contexts. Specifically, moving a software group to a hardware context would violate the exclusivity rules if both groups contain matching exclusive events.

This attempt was, however, unsuccessful: the check that we have in the perf_event_open() syscall is both wrong (looks at wrong PMU) and insufficient (group leader may still be exclusive), as can be illustrated by running:

$ perf record -e '{intel_pt//,cycles}' uname $ perf record -e '{cycles,intel_pt//}' uname

ultimately successfully.

Furthermore, we are completely free to trigger the exclusivity violation by:

perf -e '{cycles,intel_pt//}' -e '{intel_pt//,instructions}'

even though the helpful perf record will not allow that, the ABI will.

The warning later in the perf_event_open() path will also not trigger, because it's also wrong.

Fix all this by validating the original group before moving, getting rid of broken safeguards and placing a useful one to perf_install_in_context().

Signed-off-by: Alexander Shishkin alexander.shishkin@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: stable@vger.kernel.org Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: Jiri Olsa jolsa@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Stephane Eranian eranian@google.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Vince Weaver vincent.weaver@maine.edu Cc: mathieu.poirier@linaro.org Cc: will.deacon@arm.com Fixes: bed5b25ad9c8a ("perf: Add a pmu capability for "exclusive" events") Link: https://lkml.kernel.org/r/20190701110755.24646-1-alexander.shishkin@linux.in... Signed-off-by: Ingo Molnar mingo@kernel.org --- include/linux/perf_event.h | 5 +++++ kernel/events/core.c | 34 ++++++++++++++++++++++------------ 2 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 16e38c286d46..e8ad3c590a23 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -1055,6 +1055,11 @@ static inline int in_software_context(struct perf_event *event) return event->ctx->pmu->task_ctx_nr == perf_sw_context; }

+static inline int is_exclusive_pmu(struct pmu *pmu) +{ + return pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE; +} + extern struct static_key perf_swevent_enabled[PERF_COUNT_SW_MAX];

extern void ___perf_sw_event(u32, u64, struct pt_regs *, u64); diff --git a/kernel/events/core.c b/kernel/events/core.c index 5dd19bedbf64..eea9d52b010c 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2553,6 +2553,9 @@ unlock: return ret; }

+static bool exclusive_event_installable(struct perf_event *event, + struct perf_event_context *ctx); + /* * Attach a performance event to a context. * @@ -2567,6 +2570,8 @@ perf_install_in_context(struct perf_event_context *ctx,

lockdep_assert_held(&ctx->mutex);

+ WARN_ON_ONCE(!exclusive_event_installable(event, ctx)); + if (event->cpu != -1) event->cpu = cpu;

@@ -4360,7 +4365,7 @@ static int exclusive_event_init(struct perf_event *event) { struct pmu *pmu = event->pmu;

- if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE)) + if (!is_exclusive_pmu(pmu)) return 0;

/* @@ -4391,7 +4396,7 @@ static void exclusive_event_destroy(struct perf_event *event) { struct pmu *pmu = event->pmu;

- if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE)) + if (!is_exclusive_pmu(pmu)) return;

/* see comment in exclusive_event_init() */ @@ -4411,14 +4416,15 @@ static bool exclusive_event_match(struct perf_event *e1, struct perf_event *e2) return false; }

-/* Called under the same ctx::mutex as perf_install_in_context() */ static bool exclusive_event_installable(struct perf_event *event, struct perf_event_context *ctx) { struct perf_event *iter_event; struct pmu *pmu = event->pmu;

- if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE)) + lockdep_assert_held(&ctx->mutex); + + if (!is_exclusive_pmu(pmu)) return true;

list_for_each_entry(iter_event, &ctx->event_list, event_entry) { @@ -10947,11 +10953,6 @@ SYSCALL_DEFINE5(perf_event_open, goto err_alloc; }

- if ((pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE) && group_leader) { - err = -EBUSY; - goto err_context; - } - /* * Look up the group leader (we will attach this event to it): */ @@ -11039,6 +11040,18 @@ SYSCALL_DEFINE5(perf_event_open, move_group = 0; } } + + /* + * Failure to create exclusive events returns -EBUSY. + */ + err = -EBUSY; + if (!exclusive_event_installable(group_leader, ctx)) + goto err_locked; + + for_each_sibling_event(sibling, group_leader) { + if (!exclusive_event_installable(sibling, ctx)) + goto err_locked; + } } else { mutex_lock(&ctx->mutex); } @@ -11075,9 +11088,6 @@ SYSCALL_DEFINE5(perf_event_open, * because we need to serialize with concurrent event creation. */ if (!exclusive_event_installable(event, ctx)) { - /* exclusive and group stuff are assumed mutually exclusive */ - WARN_ON_ONCE(move_group); - err = -EBUSY; goto err_locked; }