| Date | Thu, 17 Jan 2013 18:02:14 -0200 | From | Herton Ronaldo Krzesinski <> | Subject | Re: [ 24/71] ring-buffer: Fix race between integrity check and readers |
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On Tue, Jan 15, 2013 at 02:54:21PM -0800, Greg Kroah-Hartman wrote: > 3.0-stable review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Steven Rostedt <srostedt@redhat.com> > > commit 9366c1ba13fbc41bdb57702e75ca4382f209c82f upstream. > > The function rb_check_pages() was added to make sure the ring buffer's > pages were sane. This check is done when the ring buffer size is modified > as well as when the iterator is released (closing the "trace" file), > as that was considered a non fast path and a good place to do a sanity > check. > > The problem is that the check does not have any locks around it. > If one process were to read the trace file, and another were to read > the raw binary file, the check could happen while the reader is reading > the file. > > The issues with this is that the check requires to clear the HEAD page > before doing the full check and it restores it afterward. But readers > require the HEAD page to exist before it can read the buffer, otherwise > it gives a nasty warning and disables the buffer. > > By adding the reader lock around the check, this keeps the race from > happening. > > Signed-off-by: Steven Rostedt <rostedt@goodmis.org> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Too late now (and harmless), but the commit id and changelog are wrong, the real commit for this backport is 54f7be5b831254199522523ccab4c3d954bbf576 (ring-buffer: Fix NULL pointer if rb_set_head_page() fails). The same happened with the patch applied on 3.4 this cycle.
-- []'s Herton
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