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: Tue, 28 May 2019 19:32:28 +0200 [thread overview]
Message-ID: <20190528173228.GW2623@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190528153224.GE20758@fuggles.cambridge.arm.com>
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().
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);
} else {
regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE;
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next prev parent reply other threads:[~2019-05-28 17:32 UTC|newest]
Thread overview: 30+ 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 12:41 ` Russell King - ARM Linux admin
2019-05-28 14:01 ` Peter Zijlstra
2019-05-28 15:32 ` Will Deacon
2019-05-28 16:12 ` Mark Rutland
2019-05-28 17:32 ` Peter Zijlstra [this message]
2019-05-29 9:17 ` Will Deacon
2019-05-29 10:10 ` Peter Zijlstra
2019-05-29 10:20 ` Will Deacon
2019-05-29 12:55 ` Peter Zijlstra
2019-05-29 13:05 ` Will Deacon
2019-05-29 13:25 ` Peter Zijlstra
2019-05-29 14:35 ` Will Deacon
2019-05-29 16:19 ` Peter Zijlstra
2019-05-29 16:24 ` Mark Rutland
2019-05-29 16:38 ` Mark Rutland
2019-05-29 17:03 ` Peter Zijlstra
2019-05-30 10:35 ` Mark Rutland
2019-05-29 16:25 ` Will Deacon
2019-05-29 16:44 ` Peter Zijlstra
2019-05-30 7:28 ` Will Deacon
2019-05-30 8:38 ` Ravi Bangoria
2019-05-30 10:27 ` Ravi Bangoria
2019-05-31 15:37 ` Will Deacon
2019-06-03 11:23 ` Will Deacon
2019-06-03 11:48 ` Peter Zijlstra
2019-06-03 13:30 ` Michael Ellerman
2019-05-29 10:11 ` Mark Rutland
2019-05-29 4:21 ` Michael Ellerman
2019-05-29 1:44 ` Michael Ellerman
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