Messages in this thread | | | Date | Mon, 26 Aug 2013 13:50:12 -0400 | From | Dave Jones <> | Subject | Re: suspicious RCU usage (perf) |
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On Mon, Aug 26, 2013 at 01:30:41PM -0400, Steven Rostedt wrote:
> > On Mon, Aug 26, 2013 at 10:58:38AM -0400, Dave Jones wrote: > > > Another day, another rcu backtrace.. > > > This says rc6, but it's pretty darn close to rc7, I think it was running > > > a build from Friday. > > > > Could you please send your .config? Also, were you running ftrace, > > perf, RCU event tracing, or what? > > > > Looks like you are running ftrace, but I though Steven had set that > > up so that it could be called from an extended quiescent state. > > > > I know exactly what the issue is. Yes ftrace is safe to call even from > these extended quiescent states, the problem is that ftrace is also the > infrastructure of other users, where some of those users are not safe. > Namely, perf. > > Right now perf is not safe to trace all functions, as some of those > functions have this issue. I was going to add something like: > > FTRACE_NON_SAFE(rcu_eqs_enter); > > where it will record locations that are not safe for all users, such > that unless a function registers to ftrace with a flag of > "FTRACE_FL_NON_SAFE_OK", anything that is on the non safe list (from > the macro) will not be traced. > > Now, how urgent is this fix? perf can only trace functions as root, and > there's no reason for perf to be tracing all functions at the moment. > But yes, a root user could run that and get this warning. Because I was > going to implement this for 3.12 and not for this release.
This was triggered as a regular user fwiw. I had not been running perf, or any other tracing. It was just left fuzzing over the weekend with no interaction at all.
Dave
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