On Tue, Sep 9, 2025 at 2:42 PM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> 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")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Feel free to add
Acked-by: Amir Goldstein <amir73il@xxxxxxxxx>
Thanks,
Amir.
> ---
> 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 184f3dc7b03b..e203b8d90fd2 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;
> --
> 2.48.1
>
