linux/kernel/trace/ring_buffer.c, branch v2.6.28

ftrace: prevent recursion

2008-11-27T09:11:53Z

Impact: prevent unnecessary stack recursion if the resched flag was set before we entered, then don't reschedule. Signed-off-by: Lai Jiangshan Acked-by: Steven Rostedt Signed-off-by: Ingo Molnar

trace: introduce missing mutex_unlock()

2008-11-18T20:37:15Z

Impact: fix tracing buffer mutex leak in case of allocation failure This error was spotted by this semantic patch: http://www.emn.fr/x-info/coccinelle/mut.html It looks correct as far as I can tell. Please review. Signed-off-by: Vegard Nossum Signed-off-by: Steven Rostedt Signed-off-by: Ingo Molnar

tracing: fix mmiotrace resizing crash

2008-11-13T13:58:31Z

Pekka reported a crash when resizing the mmiotrace tracer (if only mmiotrace is enabled). This happens because in that case we do not allocate the max buffer, but we try to use it. Make ring_buffer_resize() idempotent against NULL buffers. Reported-by: Pekka Paalanen Signed-off-by: Ingo Molnar

ring-buffer: no preempt for sched_clock()

2008-11-12T10:23:36Z

Impact: disable preemption when calling sched_clock() The ring_buffer_time_stamp still uses sched_clock as its counter. But it is a bug to call it with preemption enabled. This requirement should not be pushed to the ring_buffer_time_stamp callers, so the ring_buffer_time_stamp needs to disable preemption when calling sched_clock. Signed-off-by: Steven Rostedt Signed-off-by: Ingo Molnar

ring-buffer: buffer record on/off switch

2008-11-11T20:02:04Z

Impact: enable/disable ring buffer recording API added Several kernel developers have requested that there be a way to stop recording into the ring buffers with a simple switch that can also be enabled from userspace. This patch addes a new kernel API to the ring buffers called: tracing_on() tracing_off() When tracing_off() is called, all ring buffers will not be able to record into their buffers. tracing_on() will enable the ring buffers again. These two act like an on/off switch. That is, there is no counting of the number of times tracing_off or tracing_on has been called. A new file is added to the debugfs/tracing directory called tracing_on This allows for userspace applications to also flip the switch. echo 0 > debugfs/tracing/tracing_on disables the tracing. echo 1 > /debugfs/tracing/tracing_on enables it. Note, this does not disable or enable any tracers. It only sets or clears a flag that needs to be set in order for the ring buffers to write to their buffers. It is a global flag, and affects all ring buffers. The buffers start out with tracing_on enabled. There are now three flags that control recording into the buffers: tracing_on: which affects all ring buffer tracers. buffer->record_disabled: which affects an allocated buffer, which may be set if an anomaly is detected, and tracing is disabled. cpu_buffer->record_disabled: which is set by tracing_stop() or if an anomaly is detected. tracing_start can not reenable this if an anomaly occurred. The userspace debugfs/tracing/tracing_enabled is implemented with tracing_stop() but the user space code can not enable it if the kernel called tracing_stop(). Userspace can enable the tracing_on even if the kernel disabled it. It is just a switch used to stop tracing if a condition was hit. tracing_on is not for protecting critical areas in the kernel nor is it for stopping tracing if an anomaly occurred. This is because userspace can reenable it at any time. Side effect: With this patch, I discovered a dead variable in ftrace.c called tracing_on. This patch removes it. Signed-off-by: Steven Rostedt

ring-buffer: prevent infinite looping on time stamping

2008-11-11T02:47:37Z

Impact: removal of unnecessary looping The lockless part of the ring buffer allows for reentry into the code from interrupts. A timestamp is taken, a test is preformed and if it detects that an interrupt occurred that did tracing, it tries again. The problem arises if the timestamp code itself causes a trace. The detection will detect this and loop again. The difference between this and an interrupt doing tracing, is that this will fail every time, and cause an infinite loop. Currently, we test if the loop happens 1000 times, and if so, it will produce a warning and disable the ring buffer. The problem with this approach is that it makes it difficult to perform some types of tracing (tracing the timestamp code itself). Each trace entry has a delta timestamp from the previous entry. If a trace entry is reserved but and interrupt occurs and traces before the previous entry is commited, the delta timestamp for that entry will be zero. This actually makes sense in terms of tracing, because the interrupt entry happened before the preempted entry was commited, so one may consider the two happening at the same time. The order is still preserved in the buffer. With this idea, instead of trying to get a new timestamp if an interrupt made it in between the timestamp and the test, the entry could simply make the delta zero and continue. This will prevent interrupts or tracers in the timer code from causing the above loop. Signed-off-by: Steven Rostedt

tracing, ring-buffer: add paranoid checks for loops

2008-11-03T10:10:04Z

While writing a new tracer, I had a bug where I caused the ring-buffer to recurse in a bad way. The bug was with the tracer I was writing and not the ring-buffer itself. But it took a long time to find the problem. This patch adds paranoid checks into the ring-buffer infrastructure that will catch bugs of this nature. Note: I put the bug back in the tracer and this patch showed the error nicely and prevented the lockup. Signed-off-by: Steven Rostedt Signed-off-by: Ingo Molnar

trace: fix printk warning for u64

2008-10-27T10:31:58Z

A powerpc ppc64_defconfig build produces these warnings: kernel/trace/ring_buffer.c: In function 'rb_add_time_stamp': kernel/trace/ring_buffer.c:969: warning: format '%llu' expects type 'long long unsigned int', but argument 2 has type 'u64' kernel/trace/ring_buffer.c:969: warning: format '%llu' expects type 'long long unsigned int', but argument 3 has type 'u64' kernel/trace/ring_buffer.c:969: warning: format '%llu' expects type 'long long unsigned int', but argument 4 has type 'u64' Just cast the u64s to unsigned long long like we do everywhere else. Signed-off-by: Stephen Rothwell Acked-by: Steven Rostedt Signed-off-by: Ingo Molnar

ring-buffer: fix free page

2008-10-22T15:02:09Z

The pages of a buffer was originally pointing to the page struct, it now points to the page address. The freeing of the page still uses the page frame free "__free_page" instead of the correct free_page to the address. Signed-off-by: Steven Rostedt Signed-off-by: Ingo Molnar

ring-buffer: make reentrant

2008-10-14T08:39:19Z

This patch replaces the local_irq_save/restore with preempt_disable/ enable. This allows for interrupts to enter while recording. To write to the ring buffer, you must reserve data, and then commit it. During this time, an interrupt may call a trace function that will also record into the buffer before the commit is made. The interrupt will reserve its entry after the first entry, even though the first entry did not finish yet. The time stamp delta of the interrupt entry will be zero, since in the view of the trace, the interrupt happened during the first field anyway. Locking still takes place when the tail/write moves from one page to the next. The reader always takes the locks. A new page pointer is added, called the commit. The write/tail will always point to the end of all entries. The commit field will point to the last committed entry. Only this commit entry may update the write time stamp. The reader can only go up to the commit. It cannot go past it. If a lot of interrupts come in during a commit that fills up the buffer, and it happens to make it all the way around the buffer back to the commit, then a warning is printed and new events will be dropped. Signed-off-by: Steven Rostedt Signed-off-by: Ingo Molnar