Messages in this thread | | | Date | Wed, 15 Jul 2020 20:30:48 -0700 | From | Eric Biggers <> | Subject | Re: [PATCH 1/1] staging: android: ashmem: Fix lockdep warning for write operation |
| |
On Wed, Jul 15, 2020 at 07:45:27PM -0700, Suren Baghdasaryan wrote: > syzbot report [1] describes a deadlock when write operation against an > ashmem fd executed at the time when ashmem is shrinking its cache results > in the following lock sequence: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(fs_reclaim); > lock(&sb->s_type->i_mutex_key#13); > lock(fs_reclaim); > lock(&sb->s_type->i_mutex_key#13); > > kswapd takes fs_reclaim and then inode_lock while generic_perform_write > takes inode_lock and then fs_reclaim. However ashmem does not support > writing into backing shmem with a write syscall. The only way to change > its content is to mmap it and operate on mapped memory. Therefore the race > that lockdep is warning about is not valid. Resolve this by introducing a > separate lockdep class for the backing shmem inodes. > > [1]: https://lkml.kernel.org/lkml/0000000000000b5f9d059aa2037f@google.com/ > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Please add proper tags:
Reported-by: syzbot+7a0d9d0b26efefe61780@syzkaller.appspotmail.com Fixes: ... Cc: stable@vger.kernel.org
The Reported-by tag to use was given in the original syzbot report.
- Eric
| |