Messages in this thread Patch in this message | | | Date | Thu, 13 Aug 2009 12:50:46 -0700 | From | Greg KH <> | Subject | [patch 71/74] ring-buffer: Fix advance of reader in rb_buffer_peek() |
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2.6.30-stable review patch. If anyone has any objections, please let us know.
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From: Robert Richter <robert.richter@amd.com>
Backport for 2.6.30-stable of:
469535a 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@goodmis.org> Signed-off-by: Robert Richter <robert.richter@amd.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/trace/ring_buffer.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-)
--- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2102,7 +2102,6 @@ rb_buffer_peek(struct ring_buffer *buffe * 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: @@ -2219,6 +2218,8 @@ ring_buffer_peek(struct ring_buffer *buf again: spin_lock_irqsave(&cpu_buffer->reader_lock, flags); event = rb_buffer_peek(buffer, cpu, ts); + if (event && event->type == RINGBUF_TYPE_PADDING) + rb_advance_reader(cpu_buffer); spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); if (event && event->type == RINGBUF_TYPE_PADDING) { @@ -2283,12 +2284,9 @@ ring_buffer_consume(struct ring_buffer * spin_lock_irqsave(&cpu_buffer->reader_lock, flags); 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: spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); out:
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