the mixture of function graph tracing and kprobes.
When jprobes and function graph tracing is enabled at the same time
it will crash the system.
# modprobe jprobe_example
# echo function_graph > /sys/kernel/debug/tracing/current_tracer
After the first fork (jprobe_example probes it), the system will crash.
This is due to the way jprobes copies the stack frame and does not
do a normal function return. This messes up with the function graph
tracing accounting which hijacks the return address from the stack
and replaces it with a hook function. It saves the return addresses in
a separate stack to put back the correct return address when done.
But because the jprobe functions do not do a normal return, their
stack addresses are not put back until the function they probe is called,
which means that the probed function will get the return address of
the jprobe handler instead of its own.
The simple fix here was to disable function graph tracing while the
jprobe handler is being called.
While debugging this I found two minor bugs with the function graph
tracing.
The first was about the function graph tracer sharing its function hash
with the function tracer (they both get filtered by the same input).
The changing of the set_ftrace_filter would not sync the function recording
records after a change if the function tracer was disabled but the
function graph tracer was enabled. This was due to the update only checking
one of the ops instead of the shared ops to see if they were enabled and
should perform the sync. This caused the ftrace accounting to break and
a ftrace_bug() would be triggered, disabling ftrace until a reboot.
The second was that the check to update records only checked one of the
filter hashes. It needs to test both the "filter" and "notrace" hashes.
The "filter" hash determines what functions to trace where as the "notrace"
hash determines what functions not to trace (trace all but these).
Both hashes need to be passed to the update code to find out what change
is being done during the update. This also broke the ftrace record
accounting and triggered a ftrace_bug().
This patch set also include two more fixes that were reported separately
from the kprobe issue.
One was that init_ftrace_syscalls() was called twice at boot up.
This is not a major bug, but that call performed a rather large kmalloc
(NR_syscalls * sizeof(*syscalls_metadata)). The second call made the first
one a memory leak, and wastes memory.
The other fix is a regression caused by an update in the v3.19 merge window.
The moving to enable events early, moved the enabling before PID 1 was
created. The syscall events require setting the TIF_SYSCALL_TRACEPOINT
for all tasks. But for_each_process_thread() does not include the swapper
task (PID 0), and ended up being a nop. A suggested fix was to add
the init_task() to have its flag set, but I didn't really want to mess
with PID 0 for this minor bug. Instead I disable and re-enable events again
at early_initcall() where it use to be enabled. This also handles any other
event that might have its own reg function that could break at early
boot up.
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Merge tag 'trace-fixes-v3.19-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull ftrace fixes from Steven Rostedt:
"This holds a few fixes to the ftrace infrastructure as well as the
mixture of function graph tracing and kprobes.
When jprobes and function graph tracing is enabled at the same time it
will crash the system:
# modprobe jprobe_example
# echo function_graph > /sys/kernel/debug/tracing/current_tracer
After the first fork (jprobe_example probes it), the system will
crash.
This is due to the way jprobes copies the stack frame and does not do
a normal function return. This messes up with the function graph
tracing accounting which hijacks the return address from the stack and
replaces it with a hook function. It saves the return addresses in a
separate stack to put back the correct return address when done. But
because the jprobe functions do not do a normal return, their stack
addresses are not put back until the function they probe is called,
which means that the probed function will get the return address of
the jprobe handler instead of its own.
The simple fix here was to disable function graph tracing while the
jprobe handler is being called.
While debugging this I found two minor bugs with the function graph
tracing.
The first was about the function graph tracer sharing its function
hash with the function tracer (they both get filtered by the same
input). The changing of the set_ftrace_filter would not sync the
function recording records after a change if the function tracer was
disabled but the function graph tracer was enabled. This was due to
the update only checking one of the ops instead of the shared ops to
see if they were enabled and should perform the sync. This caused the
ftrace accounting to break and a ftrace_bug() would be triggered,
disabling ftrace until a reboot.
The second was that the check to update records only checked one of
the filter hashes. It needs to test both the "filter" and "notrace"
hashes. The "filter" hash determines what functions to trace where as
the "notrace" hash determines what functions not to trace (trace all
but these). Both hashes need to be passed to the update code to find
out what change is being done during the update. This also broke the
ftrace record accounting and triggered a ftrace_bug().
This patch set also include two more fixes that were reported
separately from the kprobe issue.
One was that init_ftrace_syscalls() was called twice at boot up. This
is not a major bug, but that call performed a rather large kmalloc
(NR_syscalls * sizeof(*syscalls_metadata)). The second call made the
first one a memory leak, and wastes memory.
The other fix is a regression caused by an update in the v3.19 merge
window. The moving to enable events early, moved the enabling before
PID 1 was created. The syscall events require setting the
TIF_SYSCALL_TRACEPOINT for all tasks. But for_each_process_thread()
does not include the swapper task (PID 0), and ended up being a nop.
A suggested fix was to add the init_task() to have its flag set, but I
didn't really want to mess with PID 0 for this minor bug. Instead I
disable and re-enable events again at early_initcall() where it use to
be enabled. This also handles any other event that might have its own
reg function that could break at early boot up"
* tag 'trace-fixes-v3.19-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
tracing: Fix enabling of syscall events on the command line
tracing: Remove extra call to init_ftrace_syscalls()
ftrace/jprobes/x86: Fix conflict between jprobes and function graph tracing
ftrace: Check both notrace and filter for old hash
ftrace: Fix updating of filters for shared global_ops filters
23aa4b416a