From: Alexander Shishkin alexander.shishkin@linux.intel.com
commit 8a58ddae23796c733c5dfbd717538d89d036c5bd upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- include/linux/perf_event.h | 5 +++++ kernel/events/core.c | 34 ++++++++++++++++++++++------------ 2 files changed, 27 insertions(+), 12 deletions(-)
--- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -1030,6 +1030,11 @@ static inline int in_software_context(st 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); --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2541,6 +2541,9 @@ unlock: return ret; }
+static bool exclusive_event_installable(struct perf_event *event, + struct perf_event_context *ctx); + /* * Attach a performance event to a context. * @@ -2555,6 +2558,8 @@ perf_install_in_context(struct perf_even
lockdep_assert_held(&ctx->mutex);
+ WARN_ON_ONCE(!exclusive_event_installable(event, ctx)); + if (event->cpu != -1) event->cpu = cpu;
@@ -4341,7 +4346,7 @@ static int exclusive_event_init(struct p { struct pmu *pmu = event->pmu;
- if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE)) + if (!is_exclusive_pmu(pmu)) return 0;
/* @@ -4372,7 +4377,7 @@ static void exclusive_event_destroy(stru { struct pmu *pmu = event->pmu;
- if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE)) + if (!is_exclusive_pmu(pmu)) return;
/* see comment in exclusive_event_init() */ @@ -4392,14 +4397,15 @@ static bool exclusive_event_match(struct 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) { @@ -10613,11 +10619,6 @@ 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): */ @@ -10705,6 +10706,18 @@ 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); } @@ -10741,9 +10754,6 @@ 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; }