diff options
author | Yang Shi <yang.shi@linux.alibaba.com> | 2020-04-20 18:14:17 -0700 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-05-02 17:25:54 +0200 |
commit | 905df10ddeb08a38c8a3fd5d19b913d08715a012 (patch) | |
tree | 04b19bbc9cb342bddcd4b9ce3d8d1f8a9d67af7f /mm | |
parent | 8e28b8489d7f6330544706abf43bd0d152781c88 (diff) |
mm: shmem: disable interrupt when acquiring info->lock in userfaultfd_copy path
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>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/shmem.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index a6fc82a1ab6b..0a2e1e7801d6 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2350,11 +2350,11 @@ 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); |