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author | Steven Rostedt <rostedt@goodmis.org> | 2015-03-17 10:40:38 -0400 |
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committer | Steven Rostedt <rostedt@goodmis.org> | 2015-03-25 08:56:49 -0400 |
commit | 80a9b64e2c156b6523e7a01f2ba6e5d86e722814 (patch) | |
tree | 9129cc167a1c9001c9edc629506c208c68c3f3e1 /kernel/trace/ring_buffer.c | |
parent | 06e5801b8cb3fc057d88cb4dc03c0b64b2744cda (diff) | |
download | linux-80a9b64e2c156b6523e7a01f2ba6e5d86e722814.tar.bz2 |
ring-buffer: Replace this_cpu_*() with __this_cpu_*()
It has come to my attention that this_cpu_read/write are horrible on
architectures other than x86. Worse yet, they actually disable
preemption or interrupts! This caused some unexpected tracing results
on ARM.
101.356868: preempt_count_add <-ring_buffer_lock_reserve
101.356870: preempt_count_sub <-ring_buffer_lock_reserve
The ring_buffer_lock_reserve has recursion protection that requires
accessing a per cpu variable. But since preempt_disable() is traced, it
too got traced while accessing the variable that is suppose to prevent
recursion like this.
The generic version of this_cpu_read() and write() are:
#define this_cpu_generic_read(pcp) \
({ typeof(pcp) ret__; \
preempt_disable(); \
ret__ = *this_cpu_ptr(&(pcp)); \
preempt_enable(); \
ret__; \
})
#define this_cpu_generic_to_op(pcp, val, op) \
do { \
unsigned long flags; \
raw_local_irq_save(flags); \
*__this_cpu_ptr(&(pcp)) op val; \
raw_local_irq_restore(flags); \
} while (0)
Which is unacceptable for locations that know they are within preempt
disabled or interrupt disabled locations.
Paul McKenney stated that __this_cpu_() versions produce much better code on
other architectures than this_cpu_() does, if we know that the call is done in
a preempt disabled location.
I also changed the recursive_unlock() to use two local variables instead
of accessing the per_cpu variable twice.
Link: http://lkml.kernel.org/r/20150317114411.GE3589@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/20150317104038.312e73d1@gandalf.local.home
Cc: stable@vger.kernel.org
Acked-by: Christoph Lameter <cl@linux.com>
Reported-by: Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>
Tested-by: Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/ring_buffer.c')
-rw-r--r-- | kernel/trace/ring_buffer.c | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 5040d44fe5a3..922048a0f7ea 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2679,7 +2679,7 @@ static DEFINE_PER_CPU(unsigned int, current_context); static __always_inline int trace_recursive_lock(void) { - unsigned int val = this_cpu_read(current_context); + unsigned int val = __this_cpu_read(current_context); int bit; if (in_interrupt()) { @@ -2696,18 +2696,17 @@ static __always_inline int trace_recursive_lock(void) return 1; val |= (1 << bit); - this_cpu_write(current_context, val); + __this_cpu_write(current_context, val); return 0; } static __always_inline void trace_recursive_unlock(void) { - unsigned int val = this_cpu_read(current_context); + unsigned int val = __this_cpu_read(current_context); - val--; - val &= this_cpu_read(current_context); - this_cpu_write(current_context, val); + val &= val & (val - 1); + __this_cpu_write(current_context, val); } #else |