6.17-stable review patch. If anyone has any objections, please let me know.
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From: Adrian Hunter adrian.hunter@intel.com
commit 8818f507a9391019a3ec7c57b1a32e4b386e48a5 upstream.
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: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/events/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9403,7 +9403,7 @@ static void perf_event_mmap_event(struct * 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;