lkml.org 
[lkml]   [2020]   [Apr]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: possible deadlock in shmem_mfill_atomic_pte
On Mon, 13 Apr 2020, Yang Shi wrote:
> On Tue, Mar 31, 2020 at 10:21 AM syzbot
> <syzbot+e27980339d305f2dbfd9@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: 527630fb Merge tag 'clk-fixes-for-linus' of git://git.kern..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1214875be00000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=27392dd2975fd692
> > dashboard link: https://syzkaller.appspot.com/bug?extid=e27980339d305f2dbfd9
> > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> >
> > Unfortunately, I don't have any reproducer for this crash yet.
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+e27980339d305f2dbfd9@syzkaller.appspotmail.com
> >
> > WARNING: possible irq lock inversion dependency detected
> > 5.6.0-rc7-syzkaller #0 Not tainted
> > --------------------------------------------------------
> > syz-executor.0/10317 just changed the state of lock:
> > ffff888021d16568 (&(&info->lock)->rlock){+.+.}, at: spin_lock include/linux/spinlock.h:338 [inline]
> > ffff888021d16568 (&(&info->lock)->rlock){+.+.}, at: shmem_mfill_atomic_pte+0x1012/0x21c0 mm/shmem.c:2407
> > but this lock was taken by another, SOFTIRQ-safe lock in the past:
> > (&(&xa->xa_lock)->rlock#5){..-.}
> >
> >
> > and interrupts could create inverse lock ordering between them.
> >
> >
> > other info that might help us debug this:
> > Possible interrupt unsafe locking scenario:
> >
> > CPU0 CPU1
> > ---- ----
> > lock(&(&info->lock)->rlock);
> > local_irq_disable();
> > lock(&(&xa->xa_lock)->rlock#5);
> > lock(&(&info->lock)->rlock);
> > <Interrupt>
> > lock(&(&xa->xa_lock)->rlock#5);
> >
> > *** DEADLOCK ***
>
> This looks possible. shmem_mfill_atomic_pte() acquires info->lock with
> irq enabled.
>
> The below patch should be able to fix it:

I agree, thank you: please send to akpm with your signoff and

Reported-by: syzbot+e27980339d305f2dbfd9@syzkaller.appspotmail.com
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Acked-by: Hugh Dickins <hughd@google.com>

I bet that 4.11 commit was being worked on before 4.8 reversed the
ordering of info->lock and tree_lock, changing spin_lock(&info->lock)s
to spin_lock_irq*(&info->lock)s - this one is the only hold-out; and
not using userfaultfd, I wouldn't have seen the lockdep report.

>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index d722eb8..762da6a 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -2399,11 +2399,11 @@ static int shmem_mfill_atomic_pte(struct
> mm_struct *dst_mm,
>
> lru_cache_add_anon(page);
>
> - spin_lock(&info->lock);
> + spin_lock_irq(&info->lock);
> info->alloced++;
> inode->i_blocks += BLOCKS_PER_PAGE;
> shmem_recalc_inode(inode);
> - spin_unlock(&info->lock);
> + spin_unlock_irq(&info->lock);
>
> inc_mm_counter(dst_mm, mm_counter_file(page));
> page_add_file_rmap(page, false);

\
 
 \ /
  Last update: 2020-04-16 03:30    [W:0.091 / U:1.584 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site