When executing the command "perf list", I met "Error: failed to open
tracing events directory" twice, the first reason is that there is no
"/sys/kernel/tracing/events" directory due to it does not enable the
kernel tracing infrastructure with CONFIG_FTRACE, the second reason
is that there is no root privileges.
Add the error string to tell the users what happened and what should
to do, and also call put_tracing_file() to free events_path a little
later to avoid messy code in the error message.
At the same time, just remove the redundant "/" of the file path in
the function get_tracing_file(), otherwise it shows something like
"/sys/kernel/tracing//events".
Before:
$ ./perf list
Error: failed to open tracing events directory
After:
(1) Without CONFIG_FTRACE
$ ./perf list
Error: failed to open tracing events directory
/sys/kernel/tracing/events: No such file or directory
(2) With CONFIG_FTRACE but no root privileges
$ ./perf list
Error: failed to open tracing events directory
/sys/kernel/tracing/events: Permission denied
Committer testing:
Redirect stdout to null to quickly test the patch:
Before:
$ perf list > /dev/null
Error: failed to open tracing events directory
$
After:
$ perf list > /dev/null
Error: failed to open tracing events directory
/sys/kernel/tracing/events: Permission denied
$
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/lkml/20240730062301.23244-3-yangtiezhu@loongson.cn
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Multiple threads, such as with "perf top", may race to initialize a
file system path like hugetlbfs. The racy initialization of the path
leads to at least memory leaks. To avoid this initialize each fs for
reading the mount point path with pthread_once.
Mounting the file system may also be racy, so introduce a mutex over
the function. This does mean that the path is being accessed with and
without a mutex, which is inherently racy but hopefully benign,
especially as there are fewer callers to fs__mount.
Remove the fs__entries by directly using global variables, this was
done as no argument like the index can be passed to the init once
routine.
Issue found and tested with "perf top" and address sanitizer.
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20230609224004.180988-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
The canonical location for the tracefs filesystem is at /sys/kernel/tracing.
But, from Documentation/trace/ftrace.rst:
Before 4.1, all ftrace tracing control files were within the debugfs
file system, which is typically located at /sys/kernel/debug/tracing.
For backward compatibility, when mounting the debugfs file system,
the tracefs file system will be automatically mounted at:
/sys/kernel/debug/tracing
Many comments and Kconfig help messages in the tracing code still refer
to this older debugfs path, so let's update them to avoid confusion.
Link: https://lore.kernel.org/linux-trace-kernel/20230215223350.2658616-2-zwisler@google.com
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>
Signed-off-by: Ross Zwisler <zwisler@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
The xxx_mountpoint() interface provided by fs.c finds mount points for
common pseudo filesystems. The first time xxx_mountpoint() is invoked,
it scans the mount table (/proc/mounts) looking for a match. If found,
it is cached. The price to scan /proc/mounts is paid once if the mount
is found.
When the mount point is not found, subsequent calls to xxx_mountpoint()
scan /proc/mounts over and over again. There is no caching.
This causes a scaling issue in perf record with hugeltbfs__mountpoint().
The function is called for each process found in
synthesize__mmap_events(). If the machine has thousands of processes
and if the /proc/mounts has many entries this could cause major overhead
in perf record. We have observed multi-second slowdowns on some
configurations.
As an example on a laptop:
Before:
$ sudo umount /dev/hugepages
$ strace -e trace=openat -o /tmp/tt perf record -a ls
$ fgrep mounts /tmp/tt
285
After:
$ sudo umount /dev/hugepages
$ strace -e trace=openat -o /tmp/tt perf record -a ls
$ fgrep mounts /tmp/tt
1
One could argue that the non-caching in case the moint point is not
found is intentional. That way subsequent calls may discover a moint
point if the sysadmin mounts the filesystem. But the same argument could
be made against caching the mount point. It could be unmounted causing
errors. It all depends on the intent of the interface. This patch
assumes it is expected to scan /proc/mounts once. The patch documents
the caching behavior in the fs.h header file.
An alternative would be to just fix perf record. But it would solve the
problem with hugetlbs__mountpoint() but there could be similar issues
(possibly down the line) with other xxx_mountpoint() calls in perf or
other tools.
Signed-off-by: Stephane Eranian <eranian@google.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andrey Zhizhikin <andrey.z@gmail.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lore.kernel.org/lkml/20200402154357.107873-3-irogers@google.com
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
If there's no tracefs (RHEL7) support the tracing_path_mount
returns debugfs path which results in following fail:
# perf probe sys_write
kprobe_events file does not exist - please rebuild kernel with CONFIG_KPROBE_EVENTS.
Error: Failed to add events.
In tracing_path_debugfs_mount function we need to return the
'tracing' path instead of just the mount to make it work:
# perf probe sys_write
Added new event:
probe:sys_write (on sys_write)
You can now use it in all perf tools, such as:
perf record -e probe:sys_write -aR sleep 1
Adding the 'return tracing_path;' also to tracing_path_tracefs_mount
function just for consistency with tracing_path_debugfs_mount.
Upstream keeps working, because it has the tracefs support.
Link: http://lkml.kernel.org/n/tip-yiwkzexq9fk1ey1xg3gnjlw4@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Fixes: 23773ca18b ("perf tools: Make perf aware of tracefs")
Link: http://lkml.kernel.org/r/20181016114818.3595-1-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
