Alexei discovered a race condition in modules failing to load that
can cause a ftrace check to trigger and disable ftrace. This is because
of the way modules are registered to ftrace. Their functions are
loaded in the ftrace function tables but set to "disabled" since
they are still in the process of being loaded by the module. After
the module is finished, it calls back into the ftrace infrastructure
to enable it. Looking deeper into the locations that access all the
functions in the table, I found more locations that should ignore
the disabled ones.
ftrace: Add more checks for FTRACE_FL_DISABLED in processing ip records
When a module is first loaded and its function ip records are added to the
ftrace list of functions to modify, they are set to DISABLED, as their text
is still in a read only state. When the module is fully loaded, and can be
updated, the flag is cleared, and if their's any functions that should be
tracing them, it is updated at that moment.
But there's several locations that do record accounting and should ignore
records that are marked as disabled, or they can cause issues.
Alexei already fixed one location, but others need to be addressed.
Cc: stable@vger.kernel.org
Fixes: b7ffffbb46f2 "ftrace: Add infrastructure for delayed enabling of module functions"
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
1 file changed
