linux-kernel - [PATCH 18/19] perf: Lift event->mmap_mutex in perf

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Message-Id: <20241104135519.582252957@infradead.org>
Date: Mon, 04 Nov 2024 14:39:27 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: mingo@...nel.org,
 lucas.demarchi@...el.com
Cc: linux-kernel@...r.kernel.org,
 peterz@...radead.org,
 willy@...radead.org,
 acme@...nel.org,
 namhyung@...nel.org,
 mark.rutland@....com,
 alexander.shishkin@...ux.intel.com,
 jolsa@...nel.org,
 irogers@...gle.com,
 adrian.hunter@...el.com,
 kan.liang@...ux.intel.com
Subject: [PATCH 18/19] perf: Lift event->mmap_mutex in perf_mmap()

This puts 'all' of perf_mmap() under single event->mmap_mutex.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/events/core.c |   20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6626,7 +6626,7 @@ static int perf_mmap(struct file *file,
 	unsigned long vma_size;
 	unsigned long nr_pages;
 	long user_extra = 0, extra = 0;
-	int ret = 0, flags = 0;
+	int ret, flags = 0;
 
 	/*
 	 * Don't allow mmap() of inherited per-task counters. This would
@@ -6654,6 +6654,9 @@ static int perf_mmap(struct file *file,
 
 	user_extra = nr_pages;
 
+	mutex_lock(&event->mmap_mutex);
+	ret = -EINVAL;
+
 	if (vma->vm_pgoff == 0) {
 		nr_pages -= 1;
 
@@ -6662,16 +6665,13 @@ static int perf_mmap(struct file *file,
 		 * can do bitmasks instead of modulo.
 		 */
 		if (nr_pages != 0 && !is_power_of_2(nr_pages))
-			return -EINVAL;
+			goto unlock;
 
 		WARN_ON_ONCE(event->ctx->parent_ctx);
-		mutex_lock(&event->mmap_mutex);
 
 		if (event->rb) {
-			if (data_page_nr(event->rb) != nr_pages) {
-				ret = -EINVAL;
+			if (data_page_nr(event->rb) != nr_pages)
 				goto unlock;
-			}
 
 			if (atomic_inc_not_zero(&event->rb->mmap_count)) {
 				/*
@@ -6698,12 +6698,6 @@ static int perf_mmap(struct file *file,
 		 */
 		u64 aux_offset, aux_size;
 
-		if (!event->rb)
-			return -EINVAL;
-
-		mutex_lock(&event->mmap_mutex);
-		ret = -EINVAL;
-
 		rb = event->rb;
 		if (!rb)
 			goto aux_unlock;
@@ -6813,6 +6807,8 @@ static int perf_mmap(struct file *file,
 			rb->aux_mmap_locked = extra;
 	}
 
+	ret = 0;
+
 unlock:
 	if (!ret) {
 		atomic_long_add(user_extra, &user->locked_vm);