Commit-ID: 469535a598f28c13a2a42037e1b778f671af1d16 Gitweb: http://git.kernel.org/tip/469535a598f28c13a2a42037e1b778f671af1d16 Author: Robert Richter <robert.richter@xxxxxxx> AuthorDate: Thu, 30 Jul 2009 19:19:18 +0200 Committer: Ingo Molnar <mingo@xxxxxxx> CommitDate: Thu, 6 Aug 2009 14:20:25 +0200 ring-buffer: Fix advance of reader in rb_buffer_peek() When calling rb_buffer_peek() from ring_buffer_consume() and a padding event is returned, the function rb_advance_reader() is called twice. This may lead to missing samples or under high workloads to the warning below. This patch fixes this. If a padding event is returned by rb_buffer_peek() it will be consumed by the calling function now. Also, I simplified some code in ring_buffer_consume(). ------------[ cut here ]------------ WARNING: at /dev/shm/.source/linux/kernel/trace/ring_buffer.c:2289 rb_advance_reader+0x2e/0xc5() Hardware name: Anaheim Modules linked in: Pid: 29, comm: events/2 Tainted: G W 2.6.31-rc3-oprofile-x86_64-standard-00059-g5050dc2 #1 Call Trace: [<ffffffff8106776f>] ? rb_advance_reader+0x2e/0xc5 [<ffffffff81039ffe>] warn_slowpath_common+0x77/0x8f [<ffffffff8103a025>] warn_slowpath_null+0xf/0x11 [<ffffffff8106776f>] rb_advance_reader+0x2e/0xc5 [<ffffffff81068bda>] ring_buffer_consume+0xa0/0xd2 [<ffffffff81326933>] op_cpu_buffer_read_entry+0x21/0x9e [<ffffffff810be3af>] ? __find_get_block+0x4b/0x165 [<ffffffff8132749b>] sync_buffer+0xa5/0x401 [<ffffffff810be3af>] ? __find_get_block+0x4b/0x165 [<ffffffff81326c1b>] ? wq_sync_buffer+0x0/0x78 [<ffffffff81326c76>] wq_sync_buffer+0x5b/0x78 [<ffffffff8104aa30>] worker_thread+0x113/0x1ac [<ffffffff8104dd95>] ? autoremove_wake_function+0x0/0x38 [<ffffffff8104a91d>] ? worker_thread+0x0/0x1ac [<ffffffff8104dc9a>] kthread+0x88/0x92 [<ffffffff8100bdba>] child_rip+0xa/0x20 [<ffffffff8104dc12>] ? kthread+0x0/0x92 [<ffffffff8100bdb0>] ? child_rip+0x0/0x20 ---[ end trace f561c0a58fcc89bd ]--- Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: <stable@xxxxxxxxxx> Signed-off-by: Robert Richter <robert.richter@xxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxx> --- kernel/trace/ring_buffer.c | 10 ++++------ 1 files changed, 4 insertions(+), 6 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 2606cee..d4d3580 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2383,7 +2383,6 @@ rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts) * the box. Return the padding, and we will release * the current locks, and try again. */ - rb_advance_reader(cpu_buffer); return event; case RINGBUF_TYPE_TIME_EXTEND: @@ -2519,6 +2518,8 @@ ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts) if (dolock) spin_lock(&cpu_buffer->reader_lock); event = rb_buffer_peek(buffer, cpu, ts); + if (event && event->type_len == RINGBUF_TYPE_PADDING) + rb_advance_reader(cpu_buffer); if (dolock) spin_unlock(&cpu_buffer->reader_lock); local_irq_restore(flags); @@ -2590,12 +2591,9 @@ ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts) spin_lock(&cpu_buffer->reader_lock); event = rb_buffer_peek(buffer, cpu, ts); - if (!event) - goto out_unlock; - - rb_advance_reader(cpu_buffer); + if (event) + rb_advance_reader(cpu_buffer); - out_unlock: if (dolock) spin_unlock(&cpu_buffer->reader_lock); local_irq_restore(flags); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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