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

JIRA: https://issues.redhat.com/browse/RHEL-179443

commit 8818f507a9391019a3ec7c57b1a32e4b386e48a5
Author: Adrian Hunter <adrian.hunter@intel.com>
Date:   Mon Oct 13 10:22:43 2025 +0300

    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@intel.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Acked-by: Amir Goldstein <amir73il@gmail.com>
    Cc: stable@vger.kernel.org

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>

kernel/events/core.c

@@ -8953,7 +8953,7 @@ 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;