From: Mark Rutland <mark.rutland@arm.com> To: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will.deacon@arm.com>, Young Xiao <92siuyang@gmail.com>, linux@armlinux.org.uk, 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 11:11:36 +0100 [thread overview] Message-ID: <20190529101135.GA31777@lakrids.cambridge.arm.com> (raw) In-Reply-To: <20190528173228.GW2623@hirez.programming.kicks-ass.net> On Tue, May 28, 2019 at 07:32:28PM +0200, Peter Zijlstra wrote: > On Tue, May 28, 2019 at 04:32:24PM +0100, Will Deacon wrote: > > On Tue, May 28, 2019 at 04:01:03PM +0200, Peter Zijlstra wrote: > > > On Tue, May 28, 2019 at 08:31:29PM +0800, Young Xiao wrote: > > > > When a kthread calls call_usermodehelper() the steps are: > > > > 1. allocate current->mm > > > > 2. load_elf_binary() > > > > 3. populate current->thread.regs > > > > > > > > While doing this, interrupts are not disabled. If there is a perf > > > > interrupt in the middle of this process (i.e. step 1 has completed > > > > but not yet reached to step 3) and if perf tries to read userspace > > > > regs, kernel oops. > > > > This seems to be because pt_regs(current) gives NULL for kthreads on Power. > > '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(). Tagnentially, it looks like that assumption is made elsewhere, and could do with a more general cleanup. IIUC, the following are suspect: * kmemleak's scan_should_stop() * x86's __kernel_fpu_begin() * arm64's arch_dup_task_struct() It's probably worth an is_thread(task) helper so that those can be written in an obviously correct way. > 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) { Wouldn't !PF_KTHREAD imply current->mm anyhow? Thanks, Mark.
WARNING: multiple messages have this Message-ID (diff)
From: Mark Rutland <mark.rutland@arm.com> To: Peter Zijlstra <peterz@infradead.org> Cc: Young Xiao <92siuyang@gmail.com>, mpe@ellerman.id.au, x86@kernel.org, Will Deacon <will.deacon@arm.com>, 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 11:11:36 +0100 [thread overview] Message-ID: <20190529101135.GA31777@lakrids.cambridge.arm.com> (raw) In-Reply-To: <20190528173228.GW2623@hirez.programming.kicks-ass.net> On Tue, May 28, 2019 at 07:32:28PM +0200, Peter Zijlstra wrote: > On Tue, May 28, 2019 at 04:32:24PM +0100, Will Deacon wrote: > > On Tue, May 28, 2019 at 04:01:03PM +0200, Peter Zijlstra wrote: > > > On Tue, May 28, 2019 at 08:31:29PM +0800, Young Xiao wrote: > > > > When a kthread calls call_usermodehelper() the steps are: > > > > 1. allocate current->mm > > > > 2. load_elf_binary() > > > > 3. populate current->thread.regs > > > > > > > > While doing this, interrupts are not disabled. If there is a perf > > > > interrupt in the middle of this process (i.e. step 1 has completed > > > > but not yet reached to step 3) and if perf tries to read userspace > > > > regs, kernel oops. > > > > This seems to be because pt_regs(current) gives NULL for kthreads on Power. > > '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(). Tagnentially, it looks like that assumption is made elsewhere, and could do with a more general cleanup. IIUC, the following are suspect: * kmemleak's scan_should_stop() * x86's __kernel_fpu_begin() * arm64's arch_dup_task_struct() It's probably worth an is_thread(task) helper so that those can be written in an obviously correct way. > 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) { Wouldn't !PF_KTHREAD imply current->mm anyhow? Thanks, Mark. _______________________________________________ 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 10:12 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 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 [this message] 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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