======================================================
[ INFO: possible circular locking dependency detected ]
4.9.144+ #77 Not tainted
-------------------------------------------------------
syz-executor286/2456 is trying to acquire lock:
 (&mm->mmap_sem){++++++}, at: [<ffffffff810b2f9b>] __do_page_fault+0x7db/0xa60 arch/x86/mm/fault.c:1342
but task is already holding lock:
 (&sb->s_type->i_mutex_key#10){+.+.+.}, at: [<ffffffff81412c1d>] inode_lock include/linux/fs.h:768 [inline]
 (&sb->s_type->i_mutex_key#10){+.+.+.}, at: [<ffffffff81412c1d>] generic_file_write_iter+0x9d/0x620 mm/filemap.c:2903
which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
       down_write+0x41/0xa0 kernel/locking/rwsem.c:52
       inode_lock include/linux/fs.h:768 [inline]
       shmem_fallocate+0x13c/0xb10 mm/shmem.c:2681
       ashmem_shrink_scan+0x1b9/0x4c0 drivers/staging/android/ashmem.c:462
       ashmem_ioctl+0x2c3/0xf00 drivers/staging/android/ashmem.c:804
       vfs_ioctl fs/ioctl.c:43 [inline]
       file_ioctl fs/ioctl.c:493 [inline]
       do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
       SYSC_ioctl fs/ioctl.c:694 [inline]
       SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
       do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
       entry_SYSCALL_64_after_swapgs+0x5d/0xdb

       lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
       __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       mutex_lock_nested+0xc0/0x900 kernel/locking/mutex.c:621
       ashmem_mmap+0x55/0x480 drivers/staging/android/ashmem.c:378
       mmap_region+0x80c/0xf90 mm/mmap.c:1726
       do_mmap+0x53d/0xbb0 mm/mmap.c:1505
       do_mmap_pgoff include/linux/mm.h:2032 [inline]
       vm_mmap_pgoff+0x168/0x1b0 mm/util.c:329
       SYSC_mmap_pgoff mm/mmap.c:1555 [inline]
       SyS_mmap_pgoff+0xfe/0x1b0 mm/mmap.c:1513
       SYSC_mmap arch/x86/kernel/sys_x86_64.c:96 [inline]
       SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:87
       do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
       entry_SYSCALL_64_after_swapgs+0x5d/0xdb

       check_prev_add kernel/locking/lockdep.c:1828 [inline]
       check_prevs_add kernel/locking/lockdep.c:1938 [inline]
       validate_chain kernel/locking/lockdep.c:2265 [inline]
       __lock_acquire+0x3189/0x4a10 kernel/locking/lockdep.c:3345
       lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
       down_read+0x44/0xb0 kernel/locking/rwsem.c:22
       __do_page_fault+0x7db/0xa60 arch/x86/mm/fault.c:1342
       do_page_fault+0x27/0x30 arch/x86/mm/fault.c:1469
       page_fault+0x25/0x30 arch/x86/entry/entry_64.S:951
       generic_perform_write+0x1c7/0x500 mm/filemap.c:2743
       __generic_file_write_iter+0x352/0x540 mm/filemap.c:2878
       generic_file_write_iter+0x37a/0x620 mm/filemap.c:2906
       new_sync_write fs/read_write.c:496 [inline]
       __vfs_write+0x3d7/0x580 fs/read_write.c:509
       vfs_write+0x187/0x520 fs/read_write.c:557
       SYSC_write fs/read_write.c:604 [inline]
       SyS_write+0xd9/0x1c0 fs/read_write.c:596
       do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
       entry_SYSCALL_64_after_swapgs+0x5d/0xdb

other info that might help us debug this:

Chain exists of:
 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sb->s_type->i_mutex_key#10);
                               lock(ashmem_mutex);
                               lock(&sb->s_type->i_mutex_key#10);
  lock(&mm->mmap_sem);

 *** DEADLOCK ***

2 locks held by syz-executor286/2456:
 #0:  (sb_writers#6){.+.+.+}, at: [<ffffffff8150b07b>] file_start_write include/linux/fs.h:2642 [inline]
 #0:  (sb_writers#6){.+.+.+}, at: [<ffffffff8150b07b>] vfs_write+0x3eb/0x520 fs/read_write.c:556
 #1:  (&sb->s_type->i_mutex_key#10){+.+.+.}, at: [<ffffffff81412c1d>] inode_lock include/linux/fs.h:768 [inline]
 #1:  (&sb->s_type->i_mutex_key#10){+.+.+.}, at: [<ffffffff81412c1d>] generic_file_write_iter+0x9d/0x620 mm/filemap.c:2903

stack backtrace:
CPU: 1 PID: 2456 Comm: syz-executor286 Not tainted 4.9.144+ #77
 ffff8801ce02f548 ffffffff81b43b89 ffffffff83cc3270 ffffffff83cae600
 ffffffff83ca4e20 ffff8801c55288f8 ffff8801c5528000 ffff8801ce02f590
 ffffffff813ff290 0000000000000002 00000000c55288d8 0000000000000002
Call Trace:
 [<ffffffff81b43b89>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81b43b89>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff813ff290>] print_circular_bug.cold.36+0x2f7/0x432 kernel/locking/lockdep.c:1202
 [<ffffffff8120a699>] check_prev_add kernel/locking/lockdep.c:1828 [inline]
 [<ffffffff8120a699>] check_prevs_add kernel/locking/lockdep.c:1938 [inline]
 [<ffffffff8120a699>] validate_chain kernel/locking/lockdep.c:2265 [inline]
 [<ffffffff8120a699>] __lock_acquire+0x3189/0x4a10 kernel/locking/lockdep.c:3345
 [<ffffffff8120ca30>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
 [<ffffffff82812aa4>] down_read+0x44/0xb0 kernel/locking/rwsem.c:22
 [<ffffffff810b2f9b>] __do_page_fault+0x7db/0xa60 arch/x86/mm/fault.c:1342
 [<ffffffff810b3277>] do_page_fault+0x27/0x30 arch/x86/mm/fault.c:1469
 [<ffffffff82819cf5>] page_fault+0x25/0x30 arch/x86/entry/entry_64.S:951
 [<ffffffff8140f987>] generic_perform_write+0x1c7/0x500 mm/filemap.c:2743
 [<ffffffff81412992>] __generic_file_write_iter+0x352/0x540 mm/filemap.c:2878
 [<ffffffff81412efa>] generic_file_write_iter+0x37a/0x620 mm/filemap.c:2906
 [<ffffffff815085c7>] new_sync_write fs/read_write.c:496 [inline]
 [<ffffffff815085c7>] __vfs_write+0x3d7/0x580 fs/read_write.c:509
 [<ffffffff8150ae17>] vfs_write+0x187/0x520 fs/read_write.c:557
 [<ffffffff8150ec49>] SYSC_write fs/read_write.c:604 [inline]
 [<ffffffff8150ec49>] SyS_write+0xd9/0x1c0 fs/read_write.c:596
 [<ffffffff810056ef>] do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
 [<ffffffff82818cd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb