Hi! Le vendredi 20 octobre 2023, 15:12:39 EEST Masami Hiramatsu a écrit : > Hi, > > Thanks for update the series. The series looks good to me. > Let me pick those in probes/fixes.
Thank you for picking it and all the good advices during the development process! > Thank you! Best regards. > On Fri, 20 Oct 2023 13:42:48 +0300 > > Francis Laniel <[email protected]> wrote: > > Hi. > > > > > > In the kernel source code, it exists different functions which share the > > same name but which have, of course, different addresses as they can be > > defined in different modules: > > # Kernel was compiled with CONFIG_NTFS_FS and CONFIG_NTFS3_FS as built-in. > > root@vm-amd64:~# grep ntfs_file_write_iter /proc/kallsyms > > ffffffff814ce3c0 t __pfx_ntfs_file_write_iter > > ffffffff814ce3d0 t ntfs_file_write_iter > > ffffffff814fc8a0 t __pfx_ntfs_file_write_iter > > ffffffff814fc8b0 t ntfs_file_write_iter > > This can be source of troubles when you create a PMU kprobe for such a > > function, as it will only install one for the first address (e.g. > > 0xffffffff814ce3d0 in the above). > > This could lead to some troubles were BPF based tools does not report any > > event because the second function is not called: > > root@vm-amd64:/mnt# mount | grep /mnt > > /foo.img on /mnt type ntfs3 (rw,relatime,uid=0,gid=0,iocharset=utf8) > > # ig is a tool which installs a PMU kprobe on ntfs_file_write_iter(). > > root@vm-amd64:/mnt# ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo & > > [1] 207 > > root@vm-amd64:/mnt# dd if=./foo of=./bar count=3 > > 3+0 records in > > 3+0 records out > > 1536 bytes (1.5 kB, 1.5 KiB) copied, 0.00543323 s, 283 kB/s > > root@vm-amd64:/mnt# fg > > ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo > > ^Croot@vm-amd64:/mnt# more /tmp/foo > > RUNTIME.CONTAINERNAME RUNTIME.CONTAIN… PID COMM > > > > T BYTES OFFSET LAT FILE > > > > 214 dd > > > > R 512 0 766 foo > > > > 214 dd > > > > R 512 512 9 foo > > > > 214 dd > > > > As you can see in the above, only read events are reported and no write > > because the kprobe is installed for the old ntfs_file_write_iter() and > > not the ntfs3 one. > > The same behavior occurs with sysfs kprobe: > > root@vm-amd64:/# echo 'p:probe/ntfs_file_write_iter ntfs_file_write_iter' > > > /sys/kernel/tracing/kprobe_events root@vm-amd64:/# cat > > /sys/kernel/tracing/kprobe_events > > p:probe/ntfs_file_write_iter ntfs_file_write_iter > > root@vm-amd64:/# mount | grep /mnt > > /foo.img on /mnt type ntfs3 (rw,relatime,uid=0,gid=0,iocharset=utf8) > > root@vm-amd64:/# perf record -e probe:ntfs_file_write_iter & > > [1] 210 > > root@vm-amd64:/# cd /mnt/ > > root@vm-amd64:/mnt# dd if=./foo of=./bar count=3 > > 3+0 records in > > 3+0 records out > > 1536 bytes (1.5 kB, 1.5 KiB) copied, 0.00234793 s, 654 kB/s > > root@vm-amd64:/mnt# cd - > > / > > root@vm-amd64:/# fg > > perf record -e probe:ntfs_file_write_iter > > ^C[ perf record: Woken up 1 times to write data ] > > [ perf record: Captured and wrote 0.056 MB perf.data ] > > > > root@vm-amd64:/# perf report > > Error: > > The perf.data data has no samples! > > # To display the perf.data header info, please use --header/--header-only > > optio> # > > > > In this contribution, I modified the functions creating sysfs and PMU > > kprobes to test if the function name given as argument matches several > > symbols. In this case, these functions return EADDRNOTAVAIL to indicate > > the user to use addr and offs to remove this ambiguity. > > So, when the above BPF tool is run, the following error message is > > printed: > > root@vm-amd64:~# ig trace fsslower -m 0 -f ntfs3 --host &> /tmp/foo & > > [1] 228 > > root@vm-amd64:~# more /tmp/foo > > RUNTIME.CONTAINERNAME RUNTIME.CONTAIN… PID COMM > > > > T BYTES OFFSET LAT FILE > > > > Error: running gadget: running gadget: installing tracer: attaching > > kprobe: crea ting perf_kprobe PMU (arch-specific fallback for > > "ntfs_file_write_iter"): token ntfs_file_write_iter: opening perf event: > > cannot assign requested address And the same with sysfs kprobe: > > root@vm-amd64:/# echo 'p:probe/ntfs_file_write_iter ntfs_file_write_iter' > > > /sys/kernel/tracing/kprobe_events -bash: echo: write error: Cannot > > assign requested address > > Note that, this does not influence perf as it installs kprobes as offset > > on > > _text: > > root@vm-amd64:/# perf probe --add ntfs_file_write_iter > > > > Added new events: > > probe:ntfs_file_write_iter (on ntfs_file_write_iter) > > probe:ntfs_file_write_iter (on ntfs_file_write_iter) > > > > ... > > root@vm-amd64:/# cat /sys/kernel/tracing/kprobe_events > > p:probe/ntfs_file_write_iter _text+5039088 > > p:probe/ntfs_file_write_iter _text+5228752 > > > > Note that, this contribution is the conclusion of a previous RFC which > > intended to install a PMU kprobe for all matching symbols [1, 2]. > > > > If you see any way to improve this contribution, please share your > > feedback.> > > Changes since: > > v1: > > * Use EADDRNOTAVAIL instead of adding a new error code. > > * Correct also this behavior for sysfs kprobe. > > > > v2: > > * Count the number of symbols corresponding to function name and return > > EADDRNOTAVAIL if higher than 1. > > * Return ENOENT if above count is 0, as it would be returned later by > > while > > registering the kprobe. > > > > v3: > > * Check symbol does not contain ':' before testing its uniqueness. > > * Add a selftest to check this is not possible to install a kprobe for a > > non unique symbol. > > > > v5: > > * No changes, just add linux-stable as recipient. > > > > v6: > > * Rephrase commit message. > > * Add "Cc:" to stable. > > > > Francis Laniel (2): > > tracing/kprobes: Return EADDRNOTAVAIL when func matches several > > > > symbols > > > > selftests/ftrace: Add new test case which checks non unique symbol > > > > kernel/trace/trace_kprobe.c | 63 +++++++++++++++++++ > > kernel/trace/trace_probe.h | 1 + > > .../test.d/kprobe/kprobe_non_uniq_symbol.tc | 13 ++++ > > 3 files changed, 77 insertions(+) > > create mode 100644 > > tools/testing/selftests/ftrace/test.d/kprobe/kprobe_non_uniq_symbol.tc> > > Best regards and thank you in advance. > > --- > > [1]: > > https://lore.kernel.org/lkml/[email protected] > > oft.com/ [2]: > > https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@kern > > el.org/ -- > > 2.34.1
