I found that having the ftrace infrastructure use its own trampoline to
handle recursion and RCU by defaulte unless the ftrace_ops set the
appropriate flags, was an issue that nobody set those flags. But then their
callbacks would suffer from an unnecessary overhead instead of simply
handling the recursion itself.
This series makes it mandatory that ftrace callbacks handle recursion or set
a flag asking ftrace to do it for it. It also creates helper functions to
help these callbacks to have recursion protection.
Changes since v1:
- Reworded the paragraph that talks about the ftrace_ops default recursion
in the change logs so that it makes more sense (recommend by Petr Mladek)
- Rebased on fixes that will be sent upstream as soon as my testing is
complete, that fixes the recursion logic. NMIs no longer trigger
false recursion positives, and also logic to handle transitions
between context that also causes false positives. These fixes are
not part of this series, but will be added before these patches.
- Added code to create a "recursed_functions" file in tracefs, that
lists the functions that triggered recursion. This was how I detected
the bugs from before. If you enable CONFIG_FTRACE_RECORD_RECURSION
it will add this logic. If you also enable FTRACE_STARTUP_TEST,
one of the tests triggers a recursion, and this will be shown in
the file after boot up (to test if it actually works).
# cat recursed_functions
ftrace_ops_assist_func+0x84/0x160:
trace_selftest_dynamic_test_func+0x0/0x10
Steven Rostedt (VMware) (11):
ftrace: Move the recursion testing into global headers
ftrace: Add ftrace_test_recursion_trylock() helper function
ftrace: Optimize testing what context current is in
pstore/ftrace: Add recursion protection to the ftrace callback
kprobes/ftrace: Add recursion protection to the ftrace callback
livepatch/ftrace: Add recursion protection to the ftrace callback
livepatch: Trigger WARNING if livepatch function fails due to recursion
perf/ftrace: Add recursion protection to the ftrace callback
perf/ftrace: Check for rcu_is_watching() in callback function
ftrace: Reverse what the RECURSION flag means in the ftrace_ops
ftrace: Add recording of functions that caused recursion
----
Documentation/trace/ftrace-uses.rst | 84 +++++++++---
arch/csky/kernel/probes/ftrace.c | 12 +-
arch/parisc/kernel/ftrace.c | 13 +-
arch/powerpc/kernel/kprobes-ftrace.c | 11 +-
arch/s390/kernel/ftrace.c | 13 +-
arch/x86/kernel/kprobes/ftrace.c | 12 +-
fs/pstore/ftrace.c | 6 +
include/linux/ftrace.h | 13 +-
include/linux/trace_recursion.h | 243 ++++++++++++++++++++++++++++++++++
kernel/livepatch/patch.c | 5 +
kernel/trace/Kconfig | 25 ++++
kernel/trace/Makefile | 1 +
kernel/trace/fgraph.c | 3 +-
kernel/trace/ftrace.c | 24 ++--
kernel/trace/trace.h | 177 -------------------------
kernel/trace/trace_event_perf.c | 13 +-
kernel/trace/trace_events.c | 1 -
kernel/trace/trace_functions.c | 14 +-
kernel/trace/trace_output.c | 6 +-
kernel/trace/trace_output.h | 1 +
kernel/trace/trace_recursion_record.c | 220 ++++++++++++++++++++++++++++++
kernel/trace/trace_selftest.c | 7 +-
kernel/trace/trace_stack.c | 1 -
23 files changed, 656 insertions(+), 249 deletions(-)
create mode 100644 include/linux/trace_recursion.h
create mode 100644 kernel/trace/trace_recursion_record.c
