user/sven/linux.git/kernel/trace/ring_buffer.c, branch v5.7.2

ring-buffer: Remove all BUG() calls

2020-05-14T12:51:02Z

There's a lot of checks to make sure the ring buffer is working, and if an anomaly is detected, it safely shuts itself down. But there's a few cases that it will call BUG(), which defeats the point of being safe (it crashes the kernel when an anomaly is found!). There's no reason for them. Switch them all to either WARN_ON_ONCE() (when no ring buffer descriptor is present), or to RB_WARN_ON() (when a ring buffer descriptor is present). Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Don't deactivate the ring buffer on failed iterator reads

2020-05-14T12:50:51Z

If the function tracer is running and the trace file is read (which uses the ring buffer iterator), the iterator can get in sync with the writes, and caues it to fail to find a page with content it can read three times. This causes a warning and deactivation of the ring buffer code. Looking at the other cases of failure to get an event, it appears that there's a chance that the writer could cause them too. Since the iterator is a "best effort" to read the ring buffer if there's an active writer (the consumer reader is made for this case "see trace_pipe"), if it fails to get an event after three tries, simply give up and return NULL. Don't warn, nor disable the ring buffer on this failure. Link: https://lore.kernel.org/r/20200429090508.GG5770@shao2-debian Reported-by: kernel test robot Fixes: ff84c50cfb4b ("ring-buffer: Do not die if rb_iter_peek() fails more than thrice") Tested-by: Sven Schnelle Signed-off-by: Steven Rostedt (VMware)

ring-buffer/tracing: Have iterator acknowledge dropped events

2020-03-27T20:39:01Z

Have the ring_buffer_iterator set a flag if events were dropped as it were to go and peek at the next event. Have the trace file display this fact if it happened with a "LOST EVENTS" message. Link: http://lkml.kernel.org/r/20200317213417.045858900@goodmis.org Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Do not disable recording when there is an iterator

2020-03-27T20:38:58Z

Now that the iterator can handle a concurrent writer, do not disable writing to the ring buffer when there is an iterator present. Link: http://lkml.kernel.org/r/20200317213416.759770696@goodmis.org Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Make resize disable per cpu buffer instead of total buffer

2020-03-27T20:21:22Z

When the ring buffer becomes writable for even when the trace file is read, it must still not be resized. But since tracers can be activated while the trace file is being read, the irqsoff tracer can modify the per CPU buffers, and this can cause the reader of the trace file to update the wrong buffer's resize disable bit, as the irqsoff tracer swaps out cpu buffers. By making the resize disable per cpu_buffer, it makes the update follow the per cpu_buffer even if it's swapped out with the snapshot buffer and keeps the release of the trace file modifying the same data as the open did. Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Optimize rb_iter_head_event()

2020-03-19T23:11:20Z

As it is fine to perform several "peeks" of event data in the ring buffer via the iterator before moving it forward, do not re-read the event, just return what was read before. Otherwise, it can cause inconsistent results, especially when testing multiple CPU buffers to interleave them. Link: http://lkml.kernel.org/r/20200317213416.592032170@goodmis.org Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Do not die if rb_iter_peek() fails more than thrice

2020-03-19T23:11:19Z

As the iterator will be reading a live buffer, and if the event being read is on a page that a writer crosses, it will fail and try again, the condition in rb_iter_peek() that only allows a retry to happen three times is no longer valid. Allow rb_iter_peek() to retry more than three times without killing the ring buffer, but only if rb_iter_head_event() had failed at least once. Link: http://lkml.kernel.org/r/20200317213416.452888193@goodmis.org Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Have rb_iter_head_event() handle concurrent writer

2020-03-19T23:11:19Z

Have the ring_buffer_iter structure have a place to store an event, such that it can not be overwritten by a writer, and load it in such a way via rb_iter_head_event() that it will return NULL and reset the iter to the start of the current page if a writer updated the page. Link: http://lkml.kernel.org/r/20200317213416.306959216@goodmis.org Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Add page_stamp to iterator for synchronization

2020-03-19T23:11:19Z

Have the ring_buffer_iter structure contain a page_stamp, such that it can be used to see if the writer entered the page the iterator is on. When going to a new page, the iterator will record the time stamp of that page. When reading events, it can copy the event to an internal buffer on the iterator (to be implemented later), then check the page's time stamp with its own to see if the writer entered the page. If so, it will need to try to read the event again. Link: http://lkml.kernel.org/r/20200317213416.163549674@goodmis.org Signed-off-by: Steven Rostedt (VMware)

ring-buffer: Rename ring_buffer_read() to read_buffer_iter_advance()

2020-03-19T23:11:19Z

When the ring buffer was first created, the iterator followed the normal producer/consumer operations where it had both a peek() operation, that just returned the event at the current location, and a read(), that would return the event at the current location and also increment the iterator such that the next peek() or read() will return the next event. The only use of the ring_buffer_read() is currently to move the iterator to the next location and nothing now actually reads the event it returns. Rename this function to its actual use case to ring_buffer_iter_advance(), which also adds the "iter" part to the name, which is more meaningful. As the timestamp returned by ring_buffer_read() was never used, there's no reason that this new version should bother having returning it. It will also become a void function. Link: http://lkml.kernel.org/r/20200317213416.018928618@goodmis.org Signed-off-by: Steven Rostedt (VMware)