OK, Jiri explained me how can I use perf to install the hwbp ;) And indeed, # perl -e 'sleep 1 while 1' & [1] 507 # perf record -e mem:0x10,mem:0x10,mem:0x10,mem:0x10,mem:0x10 -p `pidof perl` triggers the same warn/problem. Interestingly, perf record -e mem:0x10,mem:0x10,mem:0x10,mem:0x10,mem:0x10 true correctly fails with ENOSPC, this is because perf installs NR_CPUS counters for each cpu and the accounting works. IIRC, I already tried to complain that perf could be smarter in this case and install a single counter with event->cpu = -1, but this is offtopic. Oleg. On 05/28, Oleg Nesterov wrote: > > Well. I am not familiar with this code, and when I tried to read it > I feel I will be never able to understand it ;) > > On 05/20, Vince Weaver wrote: > > > > on 3.10-rc1 with the trinity fuzzer patched to exercise the > > perf_event_open() syscall I am triggering this WARN_ONCE: > > > > [ 75.864822] ------------[ cut here ]------------ > > [ 75.864830] WARNING: at arch/x86/kernel/hw_breakpoint.c:121 arch_install_hw_breakpoint+0x5b/0xcb() > ... > > [ 75.864916] [<ffffffff81006fff>] ? arch_install_hw_breakpoint+0x5b/0xcb > > [ 75.864919] [<ffffffff810ab5a1>] ? event_sched_in+0x68/0x11c > > I am wondering if we should check attr->pinned before WARN_ONCE... > > But it seems that hw_breakpoint.c is buggy anyway. > > Suppose that attr.task != NULL and event->cpu = -1. > > __reserve_bp_slot() tries to calculate slots.pinned and calls > fetch_bp_busy_slots(). > > In this case fetch_bp_busy_slots() does > > for_each_online_cpu(cpu) > ... > nr += task_bp_pinned(cpu, bp, type); > > And task_bp_pinned() (in particular) checks cpu == event->cpu, > this will be never true. > > IOW, it seems that __reserve_bp_slot(task, cpu => -1) always > succeeds because task_bp_pinned() returns 0 and thus we can > create more than HWP_NUM breakpoints. Much more ;) > > As for _create, I guess we probably need something like > > --- x/kernel/events/hw_breakpoint.c > +++ x/kernel/events/hw_breakpoint.c > @@ -156,7 +156,7 @@ fetch_bp_busy_slots(struct bp_busy_slots > if (!tsk) > nr += max_task_bp_pinned(cpu, type); > else > - nr += task_bp_pinned(cpu, bp, type); > + nr += task_bp_pinned(-1, bp, type); > > if (nr > slots->pinned) > slots->pinned = nr; > > But I simply can't understand toggle_bp_task_slot()->task_bp_pinned(). > > Oleg. -- To unsubscribe from this list: send the line "unsubscribe trinity" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
