Commit 921d4f67 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'trace-v4.15-rc4-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace 

Pull tracing fixes from Steven Rostedt:

 - Bring back context level recursive protection in ring buffer.

   The simpler counter protection failed, due to a path when tracing
   with trace_clock_global() as it could not be reentrant and depended
   on the ring buffer recursive protection to keep that from happening.

 - Prevent branch profiling when FORTIFY_SOURCE is enabled.

   It causes 50 - 60 MB in warning messages. Branch profiling should
   never be run on production systems, so there's no reason that it
   needs to be enabled with FORTIFY_SOURCE.

* tag 'trace-v4.15-rc4-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Prevent PROFILE_ALL_BRANCHES when FORTIFY_SOURCE=y
  ring-buffer: Bring back context level recursive checks
parents a8750ddc 68e76e03

kernel/trace/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -355,7 +355,7 @@ config PROFILE_ANNOTATED_BRANCHES 
	  on if you need to profile the system's use of these macros.



config PROFILE_ALL_BRANCHES

	bool "Profile all if conditionals"

	bool "Profile all if conditionals" if !FORTIFY_SOURCE

	select TRACE_BRANCH_PROFILING

	help

	  This tracer profiles all branch conditions. Every if ()

kernel/trace/ring_buffer.c

+45 −17
Original line number Diff line number Diff line
@@ -2534,29 +2534,59 @@ rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer) 
 * The lock and unlock are done within a preempt disable section.

 * The current_context per_cpu variable can only be modified

 * by the current task between lock and unlock. But it can

 * be modified more than once via an interrupt. There are four

 * different contexts that we need to consider.

 * be modified more than once via an interrupt. To pass this

 * information from the lock to the unlock without having to

 * access the 'in_interrupt()' functions again (which do show

 * a bit of overhead in something as critical as function tracing,

 * we use a bitmask trick.

 *

 *  Normal context.

 *  SoftIRQ context

 *  IRQ context

 *  NMI context

 *  bit 0 =  NMI context

 *  bit 1 =  IRQ context

 *  bit 2 =  SoftIRQ context

 *  bit 3 =  normal context.

 *

 * If for some reason the ring buffer starts to recurse, we

 * only allow that to happen at most 4 times (one for each

 * context). If it happens 5 times, then we consider this a

 * recusive loop and do not let it go further.

 * This works because this is the order of contexts that can

 * preempt other contexts. A SoftIRQ never preempts an IRQ

 * context.

 *

 * When the context is determined, the corresponding bit is

 * checked and set (if it was set, then a recursion of that context

 * happened).

 *

 * On unlock, we need to clear this bit. To do so, just subtract

 * 1 from the current_context and AND it to itself.

 *

 * (binary)

 *  101 - 1 = 100

 *  101 & 100 = 100 (clearing bit zero)

 *

 *  1010 - 1 = 1001

 *  1010 & 1001 = 1000 (clearing bit 1)

 *

 * The least significant bit can be cleared this way, and it

 * just so happens that it is the same bit corresponding to

 * the current context.

 */



static __always_inline int

trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)

{

	if (cpu_buffer->current_context >= 4)

	unsigned int val = cpu_buffer->current_context;

	unsigned long pc = preempt_count();

	int bit;



	if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))

		bit = RB_CTX_NORMAL;

	else

		bit = pc & NMI_MASK ? RB_CTX_NMI :

			pc & HARDIRQ_MASK ? RB_CTX_IRQ :

			pc & SOFTIRQ_OFFSET ? 2 : RB_CTX_SOFTIRQ;



	if (unlikely(val & (1 << bit)))

		return 1;



	cpu_buffer->current_context++;

	/* Interrupts must see this update */

	barrier();

	val |= (1 << bit);

	cpu_buffer->current_context = val;



	return 0;

}
@@ -2564,9 +2594,7 @@ trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer) 
static __always_inline void

trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)

{

	/* Don't let the dec leak out */

	barrier();

	cpu_buffer->current_context--;

	cpu_buffer->current_context &= cpu_buffer->current_context - 1;

}



/**

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