On Wed, Apr 15, 2020 at 6:27 PM Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > On Mon, 13 Apr 2020, Yang Shi wrote: > > On Tue, Mar 31, 2020 at 10:21 AM syzbot > > <syzbot+e27980339d305f2dbfd9@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > 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@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support") > Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> > > 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. Thanks, Hugh. I believe this commit could fix the splat. I'm trying to push my test tree to github to let syzkaller test it. I will send the formal patch once I get it tested. It is just slow to push to github, less than 50KB/s... > > > > > 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);
