On Fri, Sep 12, 2014 at 05:38:37PM -0700, Paul E. McKenney wrote: > On Sat, Sep 13, 2014 at 08:20:05AM +0800, Fengguang Wu wrote: > > On Fri, Sep 12, 2014 at 12:26:59PM -0700, Paul E. McKenney wrote: > > > On Fri, Sep 12, 2014 at 02:19:57PM -0500, Christoph Lameter wrote: > > > > On Fri, 12 Sep 2014, Paul E. McKenney wrote: > > > > > > > > > So, I am not seeing this failure in my testing, but my best guess is > > > > > that the problem is due to the fact that force_quiescent_state() is > > > > > sometimes invoked with preemption enabled, which breaks > > > > > __this_cpu_read() > > > > > though perhaps with very low probability. The common-case call (from > > > > > __call_rcu_core()) -does- have preemption disabled, in fact, it has > > > > > interrupts disabled. > > > > > > > > How could __this_cpu_read() break in a way that would make a difference > > > > to > > > > the code? There was no disabling/enabling of preemption before the patch > > > > and there is nothing like that after the patch. If there was a race then > > > > it still exists. The modification certainly cannot create a race. > > > > > > Excellent question. Yet Fengguang's tests show breakage. > > > > > > Fengguang, any possibility of a false positive here? > > > > Yes, it is possible. I find the first bad commit and its parent > > commit's kernels are built in 2 different machines which might > > cause subtle changes. I'll redo the bisect. > > Thank you, Fengguang, and please let me know how it goes!
The new bisect finds the below commit. However, Christoph has fixed this bug and it no longer shows up in current mainline and linux-next trees. So please ignore this noise.. commit 188a81409ff7de1c5aae947a96356ddd8ff4aaa3 Author: Christoph Lameter <[email protected]> Date: Mon Apr 7 15:39:44 2014 -0700 percpu: add preemption checks to __this_cpu ops We define a check function in order to avoid trouble with the include files. Then the higher level __this_cpu macros are modified to invoke the preemption check. [[email protected]: coding-style fixes] Signed-off-by: Christoph Lameter <[email protected]> Acked-by: Ingo Molnar <[email protected]> Cc: Tejun Heo <[email protected]> Tested-by: Grygorii Strashko <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
