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authorSteven Rostedt <rostedt@goodmis.org>2011-05-25 20:27:43 +0200
committerSteven Rostedt <rostedt@goodmis.org>2011-05-26 04:13:49 +0200
commitb1cff0ad1062621ae63cb6c5dc4165191fe2e9f1 (patch)
tree81c35a8fe57b1a139416aac637b0fc198f67199d /kernel/trace/trace.h
parenttracing: Update btrfs's tracepoints to use u64 interface (diff)
downloadlinux-b1cff0ad1062621ae63cb6c5dc4165191fe2e9f1.tar.xz
linux-b1cff0ad1062621ae63cb6c5dc4165191fe2e9f1.zip
ftrace: Add internal recursive checks
Witold reported a reboot caused by the selftests of the dynamic function tracer. He sent me a config and I used ktest to do a config_bisect on it (as my config did not cause the crash). It pointed out that the problem config was CONFIG_PROVE_RCU. What happened was that if multiple callbacks are attached to the function tracer, we iterate a list of callbacks. Because the list is managed by synchronize_sched() and preempt_disable, the access to the pointers uses rcu_dereference_raw(). When PROVE_RCU is enabled, the rcu_dereference_raw() calls some debugging functions, which happen to be traced. The tracing of the debug function would then call rcu_dereference_raw() which would then call the debug function and then... well you get the idea. I first wrote two different patches to solve this bug. 1) add a __rcu_dereference_raw() that would not do any checks. 2) add notrace to the offending debug functions. Both of these patches worked. Talking with Paul McKenney on IRC, he suggested to add recursion detection instead. This seemed to be a better solution, so I decided to implement it. As the task_struct already has a trace_recursion to detect recursion in the ring buffer, and that has a very small number it allows, I decided to use that same variable to add flags that can detect the recursion inside the infrastructure of the function tracer. I plan to change it so that the task struct bit can be checked in mcount, but as that requires changes to all archs, I will hold that off to the next merge window. Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1306348063.1465.116.camel@gandalf.stny.rr.com Reported-by: Witold Baryluk <baryluk@smp.if.uj.edu.pl> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/trace.h')
-rw-r--r--kernel/trace/trace.h15
1 files changed, 15 insertions, 0 deletions
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 6b69c4bd306f..229f8591f61d 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -784,4 +784,19 @@ extern const char *__stop___trace_bprintk_fmt[];
FTRACE_ENTRY(call, struct_name, id, PARAMS(tstruct), PARAMS(print))
#include "trace_entries.h"
+/* Only current can touch trace_recursion */
+#define trace_recursion_inc() do { (current)->trace_recursion++; } while (0)
+#define trace_recursion_dec() do { (current)->trace_recursion--; } while (0)
+
+/* Ring buffer has the 10 LSB bits to count */
+#define trace_recursion_buffer() ((current)->trace_recursion & 0x3ff)
+
+/* for function tracing recursion */
+#define TRACE_INTERNAL_BIT (1<<11)
+#define TRACE_GLOBAL_BIT (1<<12)
+
+#define trace_recursion_set(bit) do { (current)->trace_recursion |= (bit); } while (0)
+#define trace_recursion_clear(bit) do { (current)->trace_recursion &= ~(bit); } while (0)
+#define trace_recursion_test(bit) ((current)->trace_recursion & (bit))
+
#endif /* _LINUX_KERNEL_TRACE_H */