======================================================
[ INFO: possible circular locking dependency detected ]
4.4.110-g618a510 #22 Not tainted
-------------------------------------------------------
syzkaller761437/3320 is trying to acquire lock:
 (&sb->s_type->i_mutex_key#10){+.+.+.}, at: [<ffffffff814621b1>] shmem_file_llseek+0xf1/0x240 mm/shmem.c:1816

but task is already holding lock:
 (ashmem_mutex){+.+.+.}, at: [<ffffffff82c63cc6>] ashmem_llseek+0x56/0x1f0 drivers/staging/android/ashmem.c:330

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff8123c71e>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
       [<ffffffff8376c16b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8376c16b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
       [<ffffffff82c63113>] ashmem_mmap+0x53/0x400 drivers/staging/android/ashmem.c:366
       [<ffffffff814afd1f>] mmap_region+0x94f/0x1250 mm/mmap.c:1664
       [<ffffffff814b0b1d>] do_mmap+0x4fd/0x9d0 mm/mmap.c:1441
       [<ffffffff8146eece>] do_mmap_pgoff include/linux/mm.h:1915 [inline]
       [<ffffffff8146eece>] vm_mmap_pgoff+0x16e/0x1c0 mm/util.c:272
       [<ffffffff814aecef>] SYSC_mmap_pgoff mm/mmap.c:1491 [inline]
       [<ffffffff814aecef>] SyS_mmap_pgoff+0x33f/0x560 mm/mmap.c:1449
       [<ffffffff8101beb6>] SYSC_mmap arch/x86/kernel/sys_x86_64.c:95 [inline]
       [<ffffffff8101beb6>] SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:86
       [<ffffffff83775619>] entry_SYSCALL_64_fastpath+0x16/0x92

       [<ffffffff8123c71e>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
       [<ffffffff814944ea>] __might_fault+0x14a/0x1d0 mm/memory.c:3810
       [<ffffffff81559fe2>] copy_to_user arch/x86/include/asm/uaccess.h:760 [inline]
       [<ffffffff81559fe2>] filldir+0x162/0x2d0 fs/readdir.c:180
       [<ffffffff8159776e>] dir_emit_dot include/linux/fs.h:3068 [inline]
       [<ffffffff8159776e>] dir_emit_dots include/linux/fs.h:3079 [inline]
       [<ffffffff8159776e>] dcache_readdir+0x11e/0x7b0 fs/libfs.c:150
       [<ffffffff81559c28>] iterate_dir+0x1c8/0x420 fs/readdir.c:42
       [<ffffffff8155a91a>] SYSC_getdents fs/readdir.c:215 [inline]
       [<ffffffff8155a91a>] SyS_getdents+0x14a/0x270 fs/readdir.c:196
       [<ffffffff83775619>] entry_SYSCALL_64_fastpath+0x16/0x92

       [<ffffffff81239a7f>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff81239a7f>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff81239a7f>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff81239a7f>] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213
       [<ffffffff8123c71e>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
       [<ffffffff8376c16b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8376c16b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
       [<ffffffff814621b1>] shmem_file_llseek+0xf1/0x240 mm/shmem.c:1816
       [<ffffffff8151b972>] vfs_llseek+0xa2/0xd0 fs/read_write.c:260
       [<ffffffff82c63d57>] ashmem_llseek+0xe7/0x1f0 drivers/staging/android/ashmem.c:342
       [<ffffffff8151d77b>] vfs_llseek fs/read_write.c:260 [inline]
       [<ffffffff8151d77b>] SYSC_lseek fs/read_write.c:285 [inline]
       [<ffffffff8151d77b>] SyS_lseek+0xeb/0x170 fs/read_write.c:276
       [<ffffffff83775619>] entry_SYSCALL_64_fastpath+0x16/0x92

other info that might help us debug this:

Chain exists of:
 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syzkaller761437/3320:
 #0:  (ashmem_mutex){+.+.+.}, at: [<ffffffff82c63cc6>] ashmem_llseek+0x56/0x1f0 drivers/staging/android/ashmem.c:330

stack backtrace:
CPU: 0 PID: 3320 Comm: syzkaller761437 Not tainted 4.4.110-g618a510 #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 aa5bfceb4eae887a ffff8800b0e27ad8 ffffffff81d04e3d
 ffffffff8519d1c0 ffffffff851a7060 ffffffff851bb7c0 ffff8800b52d8898
 ffff8800b52d8000 ffff8800b0e27b20 ffffffff81232af1 ffff8800b52d8898
Call Trace:
 [<ffffffff81d04e3d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d04e3d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff81232af1>] print_circular_bug+0x271/0x310 kernel/locking/lockdep.c:1226
 [<ffffffff81239a7f>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff81239a7f>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff81239a7f>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff81239a7f>] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213
 [<ffffffff8123c71e>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
 [<ffffffff8376c16b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff8376c16b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621