Hi, Thanks for update the series. The series looks good to me. Let me pick those in probes/fixes.
Thank you! 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]/ > [2]: > https://lore.kernel.org/lkml/[email protected]/ > -- > 2.34.1 > -- Masami Hiramatsu (Google) <[email protected]>
