Re: [mm] 408579cd62: WARNING:suspicious_RCU_usage

[Oliver Sang]

hi, Linus,

On Sun, Jul 02, 2023 at 09:34:35PM -0700, Linus Torvalds wrote:
> On Sun, 2 Jul 2023 at 19:04, kernel test robot <oliver.sang@xxxxxxxxx> wrote:
> >
> > commit: 408579cd627a15bd703fe3eeb8485fd02726e9d3 ("mm: Update do_vmi_align_munmap() return semantics")
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> >
> > in testcase: boot
> >
> > on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> >
> > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> >
> >
> >
> > If you fix the issue, kindly add following tag
> > Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> >
> >
> > [  215.088258][    T1] WARNING: suspicious RCU usage
> 
> I think the
> 
>         validate_mm(mm);
> 
> call (mm/mmap.c:2561) needs to be moved up to before the
> 
>         if (unlock)
>                 mmap_read_unlock(mm);
> 
> that is just a couple of lines earlier.
> 
> Can you verify that that fixes the warning?

by patch [1], we found the warning is not fixed.


we also found there are some changes in stack backtrace. now it's as below:
(detail dmesg is attached)

[   26.412372][    T1] stack backtrace:
[   26.412846][    T1] CPU: 0 PID: 1 Comm: systemd Not tainted 6.4.0-09908-gcb226fb1fb7a #1
[   26.413506][    T1] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   26.414326][    T1] Call Trace:
[   26.414605][    T1]  <TASK>
[   26.414847][    T1]  dump_stack_lvl+0x73/0xc0
[   26.415225][    T1]  lockdep_rcu_suspicious+0x1b7/0x280
[   26.415669][    T1]  mas_start+0x280/0x400
[   26.416037][    T1]  mas_find+0x27a/0x400
[   26.416391][    T1]  validate_mm+0x8b/0x2c0
[   26.416757][    T1]  __se_sys_brk+0xa35/0xc00
[   26.417141][    T1]  ? vtime_user_exit+0x1a6/0x280
[   26.417563][    T1]  do_syscall_64+0x2b/0x80
[   26.417935][    T1]  entry_SYSCALL_64_after_hwframe+0x5e/0xc8
[   26.418410][    T1] RIP: 0033:0x7f8a92160bb7

as a contrast, for commit 408579cd62:

[  215.095989][    T1] stack backtrace:
[  215.097067][    T1] CPU: 0 PID: 1 Comm: init Not tainted 6.4.0-09907-g408579cd627a #1
[  215.098372][    T1] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[  215.099963][    T1] Call Trace:
[  215.100474][    T1]  <TASK>
[  215.101027][    T1]  dump_stack_lvl+0x73/0xc0
[  215.101807][    T1]  lockdep_rcu_suspicious+0x1b7/0x280
[  215.102688][    T1]  mas_start+0x280/0x400
[  215.103355][    T1]  mas_find+0x27a/0x400
[  215.104024][    T1]  validate_mm+0x8b/0x2c0
[  215.104777][    T1]  do_vmi_align_munmap+0xf92/0x1180
[  215.105691][    T1]  do_vmi_munmap+0x1a4/0x240
[  215.106384][    T1]  __vm_munmap+0x19f/0x300
[  215.107145][    T1]  __x64_sys_munmap+0x60/0x80
[  215.107962][    T1]  do_syscall_64+0x2b/0x80
[  215.108784][    T1]  entry_SYSCALL_64_after_hwframe+0x5e/0xc8
[  215.109733][    T1] RIP: 0033:0x7f5ef4577e07



[1]
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2554,11 +2554,12 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
        mas_set(&mas_detach, start);
        remove_mt(mm, &mas_detach);
        __mt_destroy(&mt_detach);
+
+       validate_mm(mm);
+
        if (unlock)
                mmap_read_unlock(mm);

-
-       validate_mm(mm);
        return 0;

 clear_tree_failed:


> 
>                  Linus

Attachment: dmesg.xz
Description: application/xz