From: "Joel Fernandes (Google)" joel@joelfernandes.org Subject: mm: shmem.c: Correctly annotate new inodes for lockdep

Directories and inodes don't necessarily need to be in the same lockdep class. For ex, hugetlbfs splits them out too to prevent false positives in lockdep. Annotate correctly after new inode creation. If its a directory inode, it will be put into a different class.

This should fix a lockdep splat reported by syzbot:

====================================================== WARNING: possible circular locking dependency detected 4.18.0-rc8-next-20180810+ #36 Not tainted

---

syz-executor900/4483 is trying to acquire lock: 00000000d2bfc8fe (&sb->s_type->i_mutex_key#9){++++}, at: inode_lock include/linux/fs.h:765 [inline] 00000000d2bfc8fe (&sb->s_type->i_mutex_key#9){++++}, at: shmem_fallocate+0x18b/0x12e0 mm/shmem.c:2602

but task is already holding lock: 0000000025208078 (ashmem_mutex){+.+.}, at: ashmem_shrink_scan+0xb4/0x630 drivers/staging/android/ashmem.c:448

which lock already depends on the new lock.

-> #2 (ashmem_mutex){+.+.}: __mutex_lock_common kernel/locking/mutex.c:925 [inline] __mutex_lock+0x171/0x1700 kernel/locking/mutex.c:1073 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1088 ashmem_mmap+0x55/0x520 drivers/staging/android/ashmem.c:361 call_mmap include/linux/fs.h:1844 [inline] mmap_region+0xf27/0x1c50 mm/mmap.c:1762 do_mmap+0xa10/0x1220 mm/mmap.c:1535 do_mmap_pgoff include/linux/mm.h:2298 [inline] vm_mmap_pgoff+0x213/0x2c0 mm/util.c:357 ksys_mmap_pgoff+0x4da/0x660 mm/mmap.c:1585 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline] __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline] __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&mm->mmap_sem){++++}: __might_fault+0x155/0x1e0 mm/memory.c:4568 _copy_to_user+0x30/0x110 lib/usercopy.c:25 copy_to_user include/linux/uaccess.h:155 [inline] filldir+0x1ea/0x3a0 fs/readdir.c:196 dir_emit_dot include/linux/fs.h:3464 [inline] dir_emit_dots include/linux/fs.h:3475 [inline] dcache_readdir+0x13a/0x620 fs/libfs.c:193 iterate_dir+0x48b/0x5d0 fs/readdir.c:51 __do_sys_getdents fs/readdir.c:231 [inline] __se_sys_getdents fs/readdir.c:212 [inline] __x64_sys_getdents+0x29f/0x510 fs/readdir.c:212 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&sb->s_type->i_mutex_key#9){++++}: lock_acquire+0x1e4/0x540 kernel/locking/lockdep.c:3924 down_write+0x8f/0x130 kernel/locking/rwsem.c:70 inode_lock include/linux/fs.h:765 [inline] shmem_fallocate+0x18b/0x12e0 mm/shmem.c:2602 ashmem_shrink_scan+0x236/0x630 drivers/staging/android/ashmem.c:455 ashmem_ioctl+0x3ae/0x13a0 drivers/staging/android/ashmem.c:797 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:501 [inline] do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702 __do_sys_ioctl fs/ioctl.c:709 [inline] __se_sys_ioctl fs/ioctl.c:707 [inline] __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of: &sb->s_type->i_mutex_key#9 --> &mm->mmap_sem --> ashmem_mutex

Possible unsafe locking scenario:

   CPU0                    CPU1
   ----                    ----

lock(ashmem_mutex); lock(&mm->mmap_sem); lock(ashmem_mutex); lock(&sb->s_type->i_mutex_key#9);

*** DEADLOCK ***

1 lock held by syz-executor900/4483: #0: 0000000025208078 (ashmem_mutex){+.+.}, at: ashmem_shrink_scan+0xb4/0x630 drivers/staging/android/ashmem.c:448

Link: http://lkml.kernel.org/r/20180821231835.166639-1-joel@joelfernandes.org Signed-off-by: Joel Fernandes (Google) joel@joelfernandes.org Reported-by: syzbot syzkaller@googlegroups.com Reviewed-by: NeilBrown neilb@suse.com Suggested-by: NeilBrown neilb@suse.com Cc: Matthew Wilcox willy@infradead.org Cc: Peter Zijlstra peterz@infradead.org Cc: Hugh Dickins hughd@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

diff -puN mm/shmem.c~mm-shmem-correctly-annotate-new-inodes-for-lockdep mm/shmem.c --- a/mm/shmem.c~mm-shmem-correctly-annotate-new-inodes-for-lockdep +++ a/mm/shmem.c @@ -2227,6 +2227,8 @@ static struct inode *shmem_get_inode(str mpol_shared_policy_init(&info->policy, NULL); break; } + + lockdep_annotate_inode_mutex_key(inode); } else shmem_free_inode(sb); return inode; _