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| author | Kumar Kartikeya Dwivedi <memxor@gmail.com> | 2026-09-26 17:45:14 +0200 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2026-09-30 14:04:05 +0200 |
| commit | 6a75c73eebd4d497ded7d08b47894f9ddbebb5a9 (patch) | |
| tree | 2bb3c750f15bcf364a61b7c46472e86f03e7b2ea | |
| parent | 7d2fa34fd3386556dbfa3867368b097cdd9b279e (diff) | |
| download | linux-next-6a75c73eebd4d497ded7d08b47894f9ddbebb5a9.tar.gz linux-next-6a75c73eebd4d497ded7d08b47894f9ddbebb5a9.zip | |
bpftool: Exit from the stream wait signal handler with _exit()
bpftool prog tracelog -w ends from its SIGINT, SIGHUP and SIGTERM handler,
which calls exit(). exit() is not async-signal-safe: it runs atexit
handlers and flushes stdio streams, and the signal may land while the read
loop is inside fwrite() or fflush() on the stream being flushed. Whether
that deadlocks or flushes a half-updated buffer depends on the C library.
Call _exit() instead. The loop flushes every chunk as soon as it is
printed, so the stdio buffer is empty except while a chunk is being
written, and skipping the exit-time flush loses nothing.
While here, note in the manual page that opening a stream as a file
descriptor arrives in Linux 7.4, and restrict the -w/--wait description to
the stdout/stderr form of the tracelog command, since the trace pipe form
does not take the option.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Quentin Monnet <qmo@kernel.org>
Link: https://lore.kernel.org/bpf/d64c6402-175f-4ea6-be6d-1a544a95c97c@qmon.net
Link: https://lore.kernel.org/bpf/20260926154515.191689-1-memxor@gmail.com
| -rw-r--r-- | tools/bpf/bpftool/Documentation/bpftool-prog.rst | 8 | ||||
| -rw-r--r-- | tools/bpf/bpftool/prog.c | 2 |
2 files changed, 6 insertions, 4 deletions
diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst index 17aa0d560e32..8dbd34ef3d8b 100644 --- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst +++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst @@ -190,7 +190,8 @@ bpftool prog tracelog { stdout | stderr } *PROG* By default, bpftool prints the output buffered so far and exits. With **-w** or **--wait**, it keeps printing new output as the program produces it, until the program is unloaded or <Ctrl+C> is hit. Waiting requires a - kernel that supports opening a stream as a file descriptor. + kernel that supports opening a stream as a file descriptor, introduced + upstream in Linux 7.4. bpftool prog run *PROG* data_in *FILE* [data_out *FILE* [data_size_out *L*]] [ctx_in *FILE* [ctx_out *FILE* [ctx_size_out *M*]]] [repeat *N*] Run BPF program *PROG* in the kernel testing infrastructure for BPF, @@ -274,8 +275,9 @@ OPTIONS signing. -w, --wait - When dumping a program stream with **bpftool prog tracelog**, wait for new - output instead of exiting once the buffered output has been printed. + When dumping a program stream with **bpftool prog tracelog** { **stdout** | + **stderr** } *PROG*, wait for new output instead of exiting once the + buffered output has been printed. EXAMPLES ======== diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c index 5e27b22444f2..a60414aaa494 100644 --- a/tools/bpf/bpftool/prog.c +++ b/tools/bpf/bpftool/prog.c @@ -1121,7 +1121,7 @@ enum prog_tracelog_mode { static void exit_stream(int signo) { - exit(0); + _exit(0); } /* Consumes prog_fd. */ |