linux-kernel - Re: BUG: using __this_cpu_read() in preemptible code in trace_hardirqs

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Date:   Tue, 13 Oct 2020 09:17:43 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     syzbot <syzbot+53f8ce8bbc07924b6417@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        syzkaller-bugs@...glegroups.com,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: BUG: using __this_cpu_read() in preemptible code in
 trace_hardirqs_on

On Tue, 13 Oct 2020 04:22:21 -0700
syzbot <syzbot+53f8ce8bbc07924b6417@...kaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    865c50e1 x86/uaccess: utilize CONFIG_CC_HAS_ASM_GOTO_OUTPUT
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15112ef0500000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c829313274207568
> dashboard link: https://syzkaller.appspot.com/bug?extid=53f8ce8bbc07924b6417
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+53f8ce8bbc07924b6417@...kaller.appspotmail.com
> 
> BUG: using __this_cpu_read() in preemptible [00000000] code: syz-executor.0/8265
> caller is lockdep_hardirqs_on_prepare+0x56/0x620 kernel/locking/lockdep.c:4060
> CPU: 0 PID: 8265 Comm: syz-executor.0 Not tainted 5.9.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1d6/0x29e lib/dump_stack.c:118
>  check_preemption_disabled+0x13c/0x140 lib/smp_processor_id.c:48
>  lockdep_hardirqs_on_prepare+0x56/0x620 kernel/locking/lockdep.c:4060
>  trace_hardirqs_on+0x6f/0x80 kernel/trace/trace_preemptirq.c:49
>  __bad_area_nosemaphore+0x89/0x510 arch/x86/mm/fault.c:797
>  handle_page_fault arch/x86/mm/fault.c:1429 [inline]
>  exc_page_fault+0x129/0x240 arch/x86/mm/fault.c:1482
>  asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:538
> RIP: 0033:0x402d28
> Code: 00 00 48 89 7c 24 f8 48 89 74 24 f0 48 89 54 24 e8 48 89 4c 24 e0 48 8b 74 24 f8 4c 8b 4c 24 f0 48 8b 4c 24 e8 48 8b 54 24 e0 <8b> 86 0c 01 00 00 44 8b 86 08 01 00 00 c1 e0 04 8d b8 7f 01 00 00
> RSP: 002b:00007fce5827ec68 EFLAGS: 00010216
> RAX: 0000000000402d00 RBX: 000000000118bfc8 RCX: 0000000020000200
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 000000000118c010 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bfd4
> R13: 00007ffea2de495f R14: 00007fce5827f9c0 R15: 000000000118bfd4
> BUG: using __this_cpu_read() in preemptible [00000000] code: syz-executor.0/8265
> caller is lockdep_hardirqs_on+0x36/0x110 kernel/locking/lockdep.c:4129
> CPU: 0 PID: 8265 Comm: syz-executor.0 Not tainted 5.9.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1d6/0x29e lib/dump_stack.c:118
>  check_preemption_disabled+0x13c/0x140 lib/smp_processor_id.c:48
>  lockdep_hardirqs_on+0x36/0x110 kernel/locking/lockdep.c:4129
>  __bad_area_nosemaphore+0x89/0x510 arch/x86/mm/fault.c:797

Peter,

I'm guessing the above is:

static void
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
		       unsigned long address, u32 pkey, int si_code)
{
	struct task_struct *tsk = current;

	/* User mode accesses just cause a SIGSEGV */
	if (user_mode(regs) && (error_code & X86_PF_USER)) {
		/*
		 * It's possible to have interrupts off here:
		 */
		local_irq_enable();


And I'm also guessing that we can call this with interrupts enabled (based
on the comment).

And we have this:

   local_irq_enable()
      trace_hardirqs_on()
         lockdep_hardirqs_on()
             __this_cpu_read()

-- Steve


>  handle_page_fault arch/x86/mm/fault.c:1429 [inline]
>  exc_page_fault+0x129/0x240 arch/x86/mm/fault.c:1482
>  asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:538
> RIP: 0033:0x402d28
> Code: 00 00 48 89 7c 24 f8 48 89 74 24 f0 48 89 54 24 e8 48 89 4c 24 e0 48 8b 74 24 f8 4c 8b 4c 24 f0 48 8b 4c 24 e8 48 8b 54 24 e0 <8b> 86 0c 01 00 00 44 8b 86 08 01 00 00 c1 e0 04 8d b8 7f 01 00 00
> RSP: 002b:00007fce5827ec68 EFLAGS: 00010216
> RAX: 0000000000402d00 RBX: 000000000118bfc8 RCX: 0000000020000200
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 000000000118c010 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bfd4
> R13: 00007ffea2de495f R14: 00007fce5827f9c0 R15: 000000000118bfd4
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
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> 
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