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@xxxxxxxxxx/ > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> Please add proper tags: Reported-by: syzbot+7a0d9d0b26efefe61780@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes: ... Cc: stable@xxxxxxxxxxxxxxx The Reported-by tag to use was given in the original syzbot report. - Eric
