From: Peter Zijlstra <peterz@infradead.org> To: Will Deacon <will.deacon@arm.com> Cc: Young Xiao <92siuyang@gmail.com>, linux@armlinux.org.uk, mark.rutland@arm.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, kan.liang@linux.intel.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, ravi.bangoria@linux.vnet.ibm.com, mpe@ellerman.id.au Subject: Re: [PATCH] perf: Fix oops when kthread execs user process Date: Wed, 29 May 2019 12:10:42 +0200 [thread overview] Message-ID: <20190529101042.GN2623@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <20190529091733.GA4485@fuggles.cambridge.arm.com> On Wed, May 29, 2019 at 10:17:33AM +0100, Will Deacon wrote: > On Tue, May 28, 2019 at 07:32:28PM +0200, Peter Zijlstra wrote: > > 'funny' thing that, perf_sample_regs_user() seems to assume that > > anything with current->mm is in fact a user task, and that assumption is > > just plain wrong, consider use_mm(). > > Right, I suppose that was attempting to handle interrupt skid from the PMU > overflow? Nah, just a broken test to determine if there is userspace at all. It is mostly right, just not completely :-) > > So I'm thinking the right thing to do here is something like the below; > > umh should get PF_KTHREAD cleared when it passes exec(). And this should > > also fix the power splat I'm thinking. > > > > --- > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index abbd4b3b96c2..9929404b6eb9 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -5923,7 +5923,7 @@ static void perf_sample_regs_user(struct perf_regs *regs_user, > > if (user_mode(regs)) { > > regs_user->abi = perf_reg_abi(current); > > regs_user->regs = regs; > > - } else if (current->mm) { > > + } else if (!(current->flags & PF_KTHREAD) && current->mm) { > > perf_get_regs_user(regs_user, regs, regs_user_copy); > > Makes sense, but under which circumstances would we have a NULL mm here? Dunno; I'm paranoid, and also: mm/memcontrol.c: if (in_interrupt() || !current->mm || (current->flags & PF_KTHREAD)) mm/vmacache.c: return current->mm == mm && !(current->flags & PF_KTHREAD);
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org> To: Will Deacon <will.deacon@arm.com> Cc: mark.rutland@arm.com, Young Xiao <92siuyang@gmail.com>, mpe@ellerman.id.au, x86@kernel.org, linux@armlinux.org.uk, linux-kernel@vger.kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, ravi.bangoria@linux.vnet.ibm.com, linux-arm-kernel@lists.infradead.org, kan.liang@linux.intel.com Subject: Re: [PATCH] perf: Fix oops when kthread execs user process Date: Wed, 29 May 2019 12:10:42 +0200 [thread overview] Message-ID: <20190529101042.GN2623@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <20190529091733.GA4485@fuggles.cambridge.arm.com> On Wed, May 29, 2019 at 10:17:33AM +0100, Will Deacon wrote: > On Tue, May 28, 2019 at 07:32:28PM +0200, Peter Zijlstra wrote: > > 'funny' thing that, perf_sample_regs_user() seems to assume that > > anything with current->mm is in fact a user task, and that assumption is > > just plain wrong, consider use_mm(). > > Right, I suppose that was attempting to handle interrupt skid from the PMU > overflow? Nah, just a broken test to determine if there is userspace at all. It is mostly right, just not completely :-) > > So I'm thinking the right thing to do here is something like the below; > > umh should get PF_KTHREAD cleared when it passes exec(). And this should > > also fix the power splat I'm thinking. > > > > --- > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index abbd4b3b96c2..9929404b6eb9 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -5923,7 +5923,7 @@ static void perf_sample_regs_user(struct perf_regs *regs_user, > > if (user_mode(regs)) { > > regs_user->abi = perf_reg_abi(current); > > regs_user->regs = regs; > > - } else if (current->mm) { > > + } else if (!(current->flags & PF_KTHREAD) && current->mm) { > > perf_get_regs_user(regs_user, regs, regs_user_copy); > > Makes sense, but under which circumstances would we have a NULL mm here? Dunno; I'm paranoid, and also: mm/memcontrol.c: if (in_interrupt() || !current->mm || (current->flags & PF_KTHREAD)) mm/vmacache.c: return current->mm == mm && !(current->flags & PF_KTHREAD); _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-05-29 10:10 UTC|newest] Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-05-28 12:31 [PATCH] perf: Fix oops when kthread execs user process Young Xiao 2019-05-28 12:31 ` Young Xiao 2019-05-28 12:41 ` Russell King - ARM Linux admin 2019-05-28 12:41 ` Russell King - ARM Linux admin 2019-05-28 14:01 ` Peter Zijlstra 2019-05-28 14:01 ` Peter Zijlstra 2019-05-28 15:32 ` Will Deacon 2019-05-28 15:32 ` Will Deacon 2019-05-28 16:12 ` Mark Rutland 2019-05-28 16:12 ` Mark Rutland 2019-05-28 17:32 ` Peter Zijlstra 2019-05-28 17:32 ` Peter Zijlstra 2019-05-29 9:17 ` Will Deacon 2019-05-29 9:17 ` Will Deacon 2019-05-29 10:10 ` Peter Zijlstra [this message] 2019-05-29 10:10 ` Peter Zijlstra 2019-05-29 10:20 ` Will Deacon 2019-05-29 10:20 ` Will Deacon 2019-05-29 12:55 ` Peter Zijlstra 2019-05-29 12:55 ` Peter Zijlstra 2019-05-29 13:05 ` Will Deacon 2019-05-29 13:05 ` Will Deacon 2019-05-29 13:25 ` Peter Zijlstra 2019-05-29 13:25 ` Peter Zijlstra 2019-05-29 14:35 ` Will Deacon 2019-05-29 14:35 ` Will Deacon 2019-05-29 16:19 ` Peter Zijlstra 2019-05-29 16:19 ` Peter Zijlstra 2019-05-29 16:24 ` Mark Rutland 2019-05-29 16:24 ` Mark Rutland 2019-05-29 16:38 ` Mark Rutland 2019-05-29 16:38 ` Mark Rutland 2019-05-29 17:03 ` Peter Zijlstra 2019-05-29 17:03 ` Peter Zijlstra 2019-05-30 10:35 ` Mark Rutland 2019-05-30 10:35 ` Mark Rutland 2019-05-29 16:25 ` Will Deacon 2019-05-29 16:25 ` Will Deacon 2019-05-29 16:44 ` Peter Zijlstra 2019-05-29 16:44 ` Peter Zijlstra 2019-05-30 7:28 ` Will Deacon 2019-05-30 7:28 ` Will Deacon 2019-05-30 8:38 ` Ravi Bangoria 2019-05-30 8:38 ` Ravi Bangoria 2019-05-30 10:27 ` Ravi Bangoria 2019-05-30 10:27 ` Ravi Bangoria 2019-05-31 15:37 ` Will Deacon 2019-05-31 15:37 ` Will Deacon 2019-06-03 11:23 ` Will Deacon 2019-06-03 11:23 ` Will Deacon 2019-06-03 11:48 ` Peter Zijlstra 2019-06-03 11:48 ` Peter Zijlstra 2019-06-03 13:30 ` Michael Ellerman 2019-06-03 13:30 ` Michael Ellerman 2019-05-29 10:11 ` Mark Rutland 2019-05-29 10:11 ` Mark Rutland 2019-05-29 4:21 ` Michael Ellerman 2019-05-29 4:21 ` Michael Ellerman 2019-05-29 1:44 ` Michael Ellerman 2019-05-29 1:44 ` Michael Ellerman
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