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While testing some new changes for 3.18, I kept hitting a bug every so

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often in the ring buffer. At first I thought it had to do with some
 of the changes I was working on, but then testing something else I
 realized that the bug was in 3.17 itself. I ran several bisects as the
 bug was not very reproducible, and finally came up with the commit
 that I could reproduce easily within a few minutes, and without the change
 I could run the tests over an hour without issue. The change fit the
 bug and I figured out a fix. That bad commit was:
 
 Commit 651e22f270 "ring-buffer: Always reset iterator to reader page"
 
 This commit fixed a bug, but in the process created another one. It used
 the wrong value as the cached value that is used to see if things changed
 while an iterator was in use. This made it look like a change always
 happened, and could cause the iterator to go into an infinite loop.
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Merge tag 'trace-fixes-v3.17-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull trace ring buffer iterator fix from Steven Rostedt:
 "While testing some new changes for 3.18, I kept hitting a bug every so
  often in the ring buffer.  At first I thought it had to do with some
  of the changes I was working on, but then testing something else I
  realized that the bug was in 3.17 itself.  I ran several bisects as
  the bug was not very reproducible, and finally came up with the commit
  that I could reproduce easily within a few minutes, and without the
  change I could run the tests over an hour without issue.  The change
  fit the bug and I figured out a fix.  That bad commit was:

    Commit 651e22f270 "ring-buffer: Always reset iterator to reader page"

  This commit fixed a bug, but in the process created another one.  It
  used the wrong value as the cached value that is used to see if things
  changed while an iterator was in use.  This made it look like a change
  always happened, and could cause the iterator to go into an infinite
  loop"

* tag 'trace-fixes-v3.17-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ring-buffer: Fix infinite spin in reading buffer
This commit is contained in:
Linus Torvalds 2014-10-03 13:31:57 -07:00
commit 039001972a
1 changed files with 1 additions and 1 deletions
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2
kernel/trace/ring_buffer.c
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@ -3359,7 +3359,7 @@ static void rb_iter_reset(struct ring_buffer_iter *iter)
iter->head = cpu_buffer->reader_page->read;
iter->cache_reader_page = iter->head_page;
iter->cache_read = iter->head;
iter->cache_read = cpu_buffer->read;
if (iter->head)
iter->read_stamp = cpu_buffer->read_stamp;