linux-kernel - [tip: perf/urgent] perf/core: Fix MMAP event path names with backing files

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Message-ID: <176043130853.709179.8229902411342716100.tip-bot2@tip-bot2>
Date: Tue, 14 Oct 2025 08:41:48 -0000
From: "tip-bot2 for Adrian Hunter" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Adrian Hunter <adrian.hunter@...el.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Amir Goldstein <amir73il@...il.com>, stable@...r.kernel.org, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: perf/urgent] perf/core: Fix MMAP event path names with backing files

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

Commit-ID:     8818f507a9391019a3ec7c57b1a32e4b386e48a5
Gitweb:        https://git.kernel.org/tip/8818f507a9391019a3ec7c57b1a32e4b386e48a5
Author:        Adrian Hunter <adrian.hunter@...el.com>
AuthorDate:    Mon, 13 Oct 2025 10:22:43 +03:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 14 Oct 2025 10:38:09 +02:00

perf/core: Fix MMAP event path names with backing files

Some file systems like FUSE-based ones or overlayfs may record the backing
file in struct vm_area_struct vm_file, instead of the user file that the
user mmapped.

Since commit def3ae83da02f ("fs: store real path instead of fake path in
backing file f_path"), file_path() no longer returns the user file path
when applied to a backing file.  There is an existing helper
file_user_path() for that situation.

Use file_user_path() instead of file_path() to get the path for MMAP
and MMAP2 events.

Example:

  Setup:

    # cd /root
    # mkdir test ; cd test ; mkdir lower upper work merged
    # cp `which cat` lower
    # mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merged
    # perf record -e intel_pt//u -- /root/test/merged/cat /proc/self/maps
    ...
    55b0ba399000-55b0ba434000 r-xp 00018000 00:1a 3419                       /root/test/merged/cat
    ...
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.060 MB perf.data ]
    #

  Before:

    File name is wrong (/cat), so decoding fails:

    # perf script --no-itrace --show-mmap-events
             cat     367 [016]   100.491492: PERF_RECORD_MMAP2 367/367: [0x55b0ba399000(0x9b000) @ 0x18000 00:02 3419 489959280]: r-xp /cat
    ...
    # perf script --itrace=e | wc -l
    Warning:
    19 instruction trace errors
    19
    #

  After:

    File name is correct (/root/test/merged/cat), so decoding is ok:

    # perf script --no-itrace --show-mmap-events
                 cat     364 [016]    72.153006: PERF_RECORD_MMAP2 364/364: [0x55ce4003d000(0x9b000) @ 0x18000 00:02 3419 3132534314]: r-xp /root/test/merged/cat
    # perf script --itrace=e
    # perf script --itrace=e | wc -l
    0
    #

Fixes: def3ae83da02f ("fs: store real path instead of fake path in backing file f_path")
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Amir Goldstein <amir73il@...il.com>
Cc: stable@...r.kernel.org
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index cd63ec8..7b5c237 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9416,7 +9416,7 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
 		 * need to add enough zero bytes after the string to handle
 		 * the 64bit alignment we do later.
 		 */
-		name = file_path(file, buf, PATH_MAX - sizeof(u64));
+		name = d_path(file_user_path(file), buf, PATH_MAX - sizeof(u64));
 		if (IS_ERR(name)) {
 			name = "//toolong";
 			goto cpy_name;