On Tue, Jun 28, 2016 at 07:19:29PM -0400, Steven Rostedt wrote: > trace_printk() is a very helpful tool for debugging the kernel. It adds > lots of tricks to optimize itself to prevent any "heisenbugs". That is, > having the addition of tracing cause the bug to change its timing and > disappear. One of this tricks is to use trace_bprintk() when possible, > which just stores the format and the arguments into the ring buffer to > be processed later at the time of reading the trace output. > > The issue with this is that there's some printf() fields that can do > redirection. There's a list of "%p*" values that will dereference the > pointer saved in the buffer. This is an issue with trace_printk() > because the pointer could have been freed between the time the > trace_printk() was called and the time the buffer is read. This will > cause a bad pointer dereference. > > The preferable fix is most likely to change bprintk() to recognize > these pointers and instead of saving the pointer in the buffer to be > processed later, it could do the conversion and save the value in the > buffer. But this added processing kills the whole point of bprintk() > from being fast and not doing any processing during the recording. > Perhaps it should simply warn and/or refuse to print. > > The simpler solution is to add an alternate trace_printk() that always > uses the non optimized version that does the string processing at the > time of the record, and saves just the string to the ring buffer. > > There's been many times that I myself wanted this version. So here it > is. > > Signed-off-by: Steven Rostedt <rost...@goodmis.org>
if we dont go with this change: http://marc.info/?l=linux-kernel&m=146715171527229&w=2 this patch works for me: Tested-by: Jiri Olsa <jo...@kernel.org> thanks, jirka
