Messages in this thread | | | Date | Tue, 16 Aug 2022 17:45:31 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH v3] perf/core: Fix reentry problem in perf_output_read_group |
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On Tue, Aug 16, 2022 at 05:39:54PM +0100, Mark Rutland wrote: > On Tue, Aug 16, 2022 at 05:31:27PM +0200, Peter Zijlstra wrote: > > On Tue, Aug 16, 2022 at 03:54:19PM +0100, Mark Rutland wrote: > > > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > > > > index ee8b9ecdc03b..d4d53b9ba71e 100644 > > > > --- a/include/linux/perf_event.h > > > > +++ b/include/linux/perf_event.h > > > > @@ -631,7 +631,12 @@ struct pmu_event_list { > > > > struct list_head list; > > > > }; > > > > > > > > +/* > > > > + * Iterating the sibling list requires this list to be stable; by ensuring IRQs > > > > + * are disabled IPIs from perf_{install_in,remove_from}_context() are held off. > > > > + */ > > > > #define for_each_sibling_event(sibling, event) \ > > > > + lockdep_assert_irqs_disabled(); \ > > > > if ((event)->group_leader == (event)) \ > > > > list_for_each_entry((sibling), &(event)->sibling_list, sibling_list) > > > > > > > > > > I had a go with v6.0-rc1 and Vince's perf fuzzer immediately triggered a bunch > > > of cases (dump below). > > > > > > I had thought holding the context mutex protected some of these cases, even > > > with IRQs unmasked? > > > > Ah yes.. duh. How's this then? > > > > > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > > index ee8b9ecdc03b..4d9cf508c510 100644 > > --- a/include/linux/perf_event.h > > +++ b/include/linux/perf_event.h > > @@ -631,7 +631,21 @@ struct pmu_event_list { > > struct list_head list; > > }; > > > > +#ifdef CONFIG_LOCKDEP > > +#define LOCKDEP_ASSERT_EVENT_CTX(event) \ > > + WARN_ON_ONCE(__lockdep_enabled && \ > > + (this_cpu_read(hardirqs_enabled) || \ > > + lockdep_is_held(&(event)->ctx->mutex) != LOCK_STATE_HELD)) > > Uh, should that `||` be `&&`, or am I missing the plot? > > This'll warn if IRQs are enabled regardless of whether the mutex is held.
With `&&` I see:
[ 25.194796] ------------[ cut here ]------------ [ 25.196017] WARNING: CPU: 0 PID: 177 at kernel/events/core.c:2231 pmu_filter_match+0x12c/0x154 [ 25.198140] Modules linked in: [ 25.198933] CPU: 0 PID: 177 Comm: perf_fuzzer Not tainted 6.0.0-rc1-00002-g2dee3ea2f881 #9 [ 25.200945] Hardware name: linux,dummy-virt (DT) [ 25.202083] pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 25.203799] pc : pmu_filter_match+0x12c/0x154 [ 25.204881] lr : pmu_filter_match+0x124/0x154 [ 25.205964] sp : ffff80000b753a90 [ 25.206807] x29: ffff80000b753a90 x28: 0000000001200000 x27: 0000000000000000 [ 25.208557] x26: ffff00000523ca40 x25: ffff80000a90bbd0 x24: 0000000000000000 [ 25.210316] x23: ffff800009d92008 x22: ffff8000082669a0 x21: ffff80000b753b58 [ 25.212065] x20: ffff000005890560 x19: 0000000000000001 x18: 0000000000000001 [ 25.213819] x17: 00000000c3d5f54b x16: 000000006eb75123 x15: 00000000000000dc [ 25.215574] x14: 0000000001200011 x13: 0000000060000000 x12: 0000000000000015 [ 25.217325] x11: 0000000000000015 x10: 000007ffffffffff x9 : 00000000ffffffff [ 25.219091] x8 : ffff80000a910718 x7 : 0000000000000000 x6 : 0000000000000001 [ 25.220847] x5 : 00000000c3affd79 x4 : 0000000000000000 x3 : ffff000003b15800 [ 25.222605] x2 : 0000000000000001 x1 : 00000000000000c0 x0 : 0000000000000000 [ 25.224361] Call trace: [ 25.224987] pmu_filter_match+0x12c/0x154 [ 25.225987] perf_iterate_ctx+0x110/0x11c [ 25.226997] perf_iterate_sb+0x258/0x2f0 [ 25.227971] perf_event_fork+0x74/0xc0 [ 25.228910] copy_process+0x1484/0x1964 [ 25.229869] kernel_clone+0x9c/0x4a4 [ 25.230780] __do_sys_clone+0x70/0xac [ 25.231699] __arm64_sys_clone+0x24/0x30 [ 25.232679] invoke_syscall+0x48/0x114 [ 25.233615] el0_svc_common.constprop.0+0x60/0x11c [ 25.234817] do_el0_svc+0x30/0xc0 [ 25.235659] el0_svc+0x48/0xc0 [ 25.236438] el0t_64_sync_handler+0x120/0x15c [ 25.237523] el0t_64_sync+0x18c/0x190 [ 25.238448] irq event stamp: 13502 [ 25.239301] hardirqs last enabled at (13501): [<ffff8000091f0d68>] _raw_spin_unlock_irqrestore+0x88/0x94 [ 25.241627] hardirqs last disabled at (13502): [<ffff8000091e42d4>] el1_dbg+0x24/0x90 [ 25.243550] softirqs last enabled at (13340): [<ffff800008016e98>] put_cpu_fpsimd_context+0x28/0x70 [ 25.245773] softirqs last disabled at (13338): [<ffff800008016e14>] get_cpu_fpsimd_context+0x0/0x5c [ 25.247989] ---[ end trace 0000000000000000 ]---
Thanks, Mark.
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