6.18-stable review patch. If anyone has any objections, please let me know.
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From: Thaumy Cheng thaumy.love@gmail.com
[ Upstream commit c418d8b4d7a43a86b82ee39cb52ece3034383530 ]
For events with inherit_stat enabled, a "read" event will be generated to collect per task event counts on task exit.
The call chain is as follows:
do_exit -> perf_event_exit_task -> perf_event_exit_task_context -> perf_event_exit_event -> perf_remove_from_context -> perf_child_detach -> sync_child_event -> perf_event_read_event
However, the child event context detaches the task too early in perf_event_exit_task_context, which causes sync_child_event to never generate the read event in this case, since child_event->ctx->task is always set to TASK_TOMBSTONE. Fix that by moving context lock section backward to ensure ctx->task is not set to TASK_TOMBSTONE before generating the read event.
Because perf_event_free_task calls perf_event_exit_task_context with exit = false to tear down all child events from the context, and the task never lived, accessing the task PID can lead to a use-after-free.
To fix that, let sync_child_event read task from argument and move the call to the only place it should be triggered to avoid the effect of setting ctx->task to TASK_TOMESTONE, and add a task parameter to perf_event_exit_event to trigger the sync_child_event properly when needed.
This bug can be reproduced by running "perf record -s" and attaching to any program that generates perf events in its child tasks. If we check the result with "perf report -T", the last line of the report will leave an empty table like "# PID TID", which is expected to contain the per-task event counts by design.
Fixes: ef54c1a476ae ("perf: Rework perf_event_exit_event()") Signed-off-by: Thaumy Cheng thaumy.love@gmail.com Signed-off-by: Ingo Molnar mingo@kernel.org Acked-by: Peter Zijlstra peterz@infradead.org Cc: Adrian Hunter adrian.hunter@intel.com Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Arnaldo Carvalho de Melo acme@kernel.org Cc: Ian Rogers irogers@google.com Cc: James Clark james.clark@linaro.org Cc: Jiri Olsa jolsa@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Namhyung Kim namhyung@kernel.org Cc: linux-perf-users@vger.kernel.org Link: https://patch.msgid.link/20251209041600.963586-1-thaumy.love@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/events/core.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 2c35acc2722b0..413b88a4e00fb 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2316,8 +2316,6 @@ static void perf_group_detach(struct perf_event *event) perf_event__header_size(leader); }
-static void sync_child_event(struct perf_event *child_event); - static void perf_child_detach(struct perf_event *event) { struct perf_event *parent_event = event->parent; @@ -2336,7 +2334,6 @@ static void perf_child_detach(struct perf_event *event) lockdep_assert_held(&parent_event->child_mutex); */
- sync_child_event(event); list_del_init(&event->child_list); }
@@ -4587,6 +4584,7 @@ static void perf_event_enable_on_exec(struct perf_event_context *ctx) static void perf_remove_from_owner(struct perf_event *event); static void perf_event_exit_event(struct perf_event *event, struct perf_event_context *ctx, + struct task_struct *task, bool revoke);
/* @@ -4614,7 +4612,7 @@ static void perf_event_remove_on_exec(struct perf_event_context *ctx)
modified = true;
- perf_event_exit_event(event, ctx, false); + perf_event_exit_event(event, ctx, ctx->task, false); }
raw_spin_lock_irqsave(&ctx->lock, flags); @@ -12447,7 +12445,7 @@ static void __pmu_detach_event(struct pmu *pmu, struct perf_event *event, /* * De-schedule the event and mark it REVOKED. */ - perf_event_exit_event(event, ctx, true); + perf_event_exit_event(event, ctx, ctx->task, true);
/* * All _free_event() bits that rely on event->pmu: @@ -14004,14 +14002,13 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu) } EXPORT_SYMBOL_GPL(perf_pmu_migrate_context);
-static void sync_child_event(struct perf_event *child_event) +static void sync_child_event(struct perf_event *child_event, + struct task_struct *task) { struct perf_event *parent_event = child_event->parent; u64 child_val;
if (child_event->attr.inherit_stat) { - struct task_struct *task = child_event->ctx->task; - if (task && task != TASK_TOMBSTONE) perf_event_read_event(child_event, task); } @@ -14030,7 +14027,9 @@ static void sync_child_event(struct perf_event *child_event)
static void perf_event_exit_event(struct perf_event *event, - struct perf_event_context *ctx, bool revoke) + struct perf_event_context *ctx, + struct task_struct *task, + bool revoke) { struct perf_event *parent_event = event->parent; unsigned long detach_flags = DETACH_EXIT; @@ -14053,6 +14052,9 @@ perf_event_exit_event(struct perf_event *event, mutex_lock(&parent_event->child_mutex); /* PERF_ATTACH_ITRACE might be set concurrently */ attach_state = READ_ONCE(event->attach_state); + + if (attach_state & PERF_ATTACH_CHILD) + sync_child_event(event, task); }
if (revoke) @@ -14144,7 +14146,7 @@ static void perf_event_exit_task_context(struct task_struct *task, bool exit) perf_event_task(task, ctx, 0);
list_for_each_entry_safe(child_event, next, &ctx->event_list, event_entry) - perf_event_exit_event(child_event, ctx, false); + perf_event_exit_event(child_event, ctx, exit ? task : NULL, false);
mutex_unlock(&ctx->mutex);