linux-kernel - [tip: perf/urgent] perf/core: Fix perf_mmap fail when CONFIG_PERF_USE

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Date:   Tue, 19 Apr 2022 19:34:44 -0000
From:   "tip-bot2 for Zhipeng Xie" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Zhipeng Xie <xiezhipeng1@...wei.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/core: Fix perf_mmap fail when
 CONFIG_PERF_USE_VMALLOC enabled

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     60490e7966659b26d74bf1fa4aa8693d9a94ca88
Gitweb:        https://git.kernel.org/tip/60490e7966659b26d74bf1fa4aa8693d9a94ca88
Author:        Zhipeng Xie <xiezhipeng1@...wei.com>
AuthorDate:    Wed, 09 Feb 2022 09:54:17 -05:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 19 Apr 2022 21:15:42 +02:00

perf/core: Fix perf_mmap fail when CONFIG_PERF_USE_VMALLOC enabled

This problem can be reproduced with CONFIG_PERF_USE_VMALLOC enabled on
both x86_64 and aarch64 arch when using sysdig -B(using ebpf)[1].
sysdig -B works fine after rebuilding the kernel with
CONFIG_PERF_USE_VMALLOC disabled.

I tracked it down to the if condition event->rb->nr_pages != nr_pages
in perf_mmap is true when CONFIG_PERF_USE_VMALLOC is enabled where
event->rb->nr_pages = 1 and nr_pages = 2048 resulting perf_mmap to
return -EINVAL. This is because when CONFIG_PERF_USE_VMALLOC is
enabled, rb->nr_pages is always equal to 1.

Arch with CONFIG_PERF_USE_VMALLOC enabled by default:
	arc/arm/csky/mips/sh/sparc/xtensa

Arch with CONFIG_PERF_USE_VMALLOC disabled by default:
	x86_64/aarch64/...

Fix this problem by using data_page_nr()

[1] https://github.com/draios/sysdig

Fixes: 906010b2134e ("perf_event: Provide vmalloc() based mmap() backing")
Signed-off-by: Zhipeng Xie <xiezhipeng1@...wei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20220209145417.6495-1-xiezhipeng1@huawei.com
---
 kernel/events/core.c        | 2 +-
 kernel/events/internal.h    | 5 +++++
 kernel/events/ring_buffer.c | 5 -----
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 23bb197..7858baf 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6247,7 +6247,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 again:
 	mutex_lock(&event->mmap_mutex);
 	if (event->rb) {
-		if (event->rb->nr_pages != nr_pages) {
+		if (data_page_nr(event->rb) != nr_pages) {
 			ret = -EINVAL;
 			goto unlock;
 		}
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 0828327..5150d5f 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -116,6 +116,11 @@ static inline int page_order(struct perf_buffer *rb)
 }
 #endif
 
+static inline int data_page_nr(struct perf_buffer *rb)
+{
+	return rb->nr_pages << page_order(rb);
+}
+
 static inline unsigned long perf_data_size(struct perf_buffer *rb)
 {
 	return rb->nr_pages << (PAGE_SHIFT + page_order(rb));
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 5286871..fb35b92 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -859,11 +859,6 @@ void rb_free(struct perf_buffer *rb)
 }
 
 #else
-static int data_page_nr(struct perf_buffer *rb)
-{
-	return rb->nr_pages << page_order(rb);
-}
-
 static struct page *
 __perf_mmap_to_page(struct perf_buffer *rb, unsigned long pgoff)
 {