Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.14 097/117] mm: shmem: disable interrupt when acquiring info->lock in userfaultfd_copy path | Date | Fri, 1 May 2020 15:22:13 +0200 |
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From: Yang Shi <yang.shi@linux.alibaba.com>
commit 94b7cc01da5a3cc4f3da5e0ff492ef008bb555d6 upstream.
Syzbot reported the below lockdep splat:
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 ***
The full report is quite lengthy, please see:
https://lore.kernel.org/linux-mm/alpine.LSU.2.11.2004152007370.13597@eggly.anvils/T/#m813b412c5f78e25ca8c6c7734886ed4de43f241d
It is because CPU 0 held info->lock with IRQ enabled in userfaultfd_copy path, then CPU 1 is splitting a THP which held xa_lock and info->lock in IRQ disabled context at the same time. If softirq comes in to acquire xa_lock, the deadlock would be triggered.
The fix is to acquire/release info->lock with *_irq version instead of plain spin_{lock,unlock} to make it softirq safe.
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support") Reported-by: syzbot+e27980339d305f2dbfd9@syzkaller.appspotmail.com Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: syzbot+e27980339d305f2dbfd9@syzkaller.appspotmail.com Acked-by: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Link: http://lkml.kernel.org/r/1587061357-122619-1-git-send-email-yang.shi@linux.alibaba.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/shmem.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/shmem.c +++ b/mm/shmem.c @@ -2330,11 +2330,11 @@ static int shmem_mfill_atomic_pte(struct 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);
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