syzbot

======================================================
[ INFO: possible circular locking dependency detected ]
4.9.81-ga25ea24 #36 Not tainted
-------------------------------------------------------
syz-executor3/5271 is trying to acquire lock:
 (&sb->s_type->i_mutex_key#10){++++++}
but task is already holding lock:
 (ashmem_mutex){+.+.+.}, at: [<ffffffff82d497a6>] ashmem_llseek+0x56/0x1f0 drivers/staging/android/ashmem.c:343
which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2
 (ashmem_mutex){+.+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       mutex_lock_nested+0xbb/0x870 kernel/locking/mutex.c:621
       ashmem_mmap+0x53/0x400 drivers/staging/android/ashmem.c:379
       mmap_region+0x7dd/0xfd0 mm/mmap.c:1694
       do_mmap+0x57b/0xbe0 mm/mmap.c:1473
       do_mmap_pgoff include/linux/mm.h:2019 [inline]
       vm_mmap_pgoff+0x16b/0x1b0 mm/util.c:305
       SYSC_mmap_pgoff mm/mmap.c:1523 [inline]
       SyS_mmap_pgoff+0x33f/0x560 mm/mmap.c:1481
       SYSC_mmap arch/x86/kernel/sys_x86_64.c:95 [inline]
       SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:86
       do_syscall_64+0x1a5/0x490 arch/x86/entry/common.c:282
       entry_SYSCALL_64_after_swapgs+0x47/0xc5

-> #1
 (&mm->mmap_sem){++++++}:
       __might_fault+0x14a/0x1d0 mm/memory.c:3994
       copy_to_user arch/x86/include/asm/uaccess.h:727 [inline]
       filldir+0x1aa/0x340 fs/readdir.c:195
       dir_emit_dot include/linux/fs.h:3203 [inline]
       dir_emit_dots include/linux/fs.h:3214 [inline]
       dcache_readdir+0x12d/0x5e0 fs/libfs.c:191
       iterate_dir+0x4a6/0x5d0 fs/readdir.c:50
       SYSC_getdents fs/readdir.c:230 [inline]
       SyS_getdents+0x14a/0x2a0 fs/readdir.c:211
       do_syscall_64+0x1a5/0x490 arch/x86/entry/common.c:282
       entry_SYSCALL_64_after_swapgs+0x47/0xc5

-> #0
 (&sb->s_type->i_mutex_key#10){++++++}:
       lock_acquire+0x12e/0x410 kernel/locking/lockdep.c:3756
       down_write+0x41/0xa0 kernel/locking/rwsem.c:52
       inode_lock include/linux/fs.h:746 [inline]
       shmem_file_llseek+0xef/0x240 mm/shmem.c:2403
       vfs_llseek+0xa2/0xd0 fs/read_write.c:301
       ashmem_llseek+0xe7/0x1f0 drivers/staging/android/ashmem.c:355
       vfs_llseek fs/read_write.c:301 [inline]
       SYSC_lseek fs/read_write.c:314 [inline]
       SyS_lseek+0xeb/0x170 fs/read_write.c:305
       do_syscall_64+0x1a5/0x490 arch/x86/entry/common.c:282
       entry_SYSCALL_64_after_swapgs+0x47/0xc5

other info that might help us debug this:

Chain exists of:
  
&sb->s_type->i_mutex_key#10 --> &mm->mmap_sem --> ashmem_mutex


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

1 lock held by syz-executor3/5271:
 #0: 
 (ashmem_mutex){+.+.+.}, at: [<ffffffff82d497a6>] ashmem_llseek+0x56/0x1f0 drivers/staging/android/ashmem.c:343
stack backtrace:
CPU: 0 PID: 5271 Comm: syz-executor3 Not tainted 4.9.81-ga25ea24 #36
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801b8e37b38
 ffffffff81d94de9 ffffffff853a2b20 ffffffff853ac810 ffffffff853c3130
 ffff8801b613e8d8 ffff8801b613e000 ffff8801b8e37b80 ffffffff81238741
 ffff8801b613e8d8 00000000b613e8b0 ffff8801b613e8d8Call Trace:
 [<ffffffff81d94de9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d94de9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81238741>] print_circular_bug+0x271/0x310 kernel/locking/lockdep.c:1202
 [<ffffffff8123eb79>] check_prev_add kernel/locking/lockdep.c:1828 [inline]
 [<ffffffff8123eb79>] check_prevs_add kernel/locking/lockdep.c:1938 [inline]
 [<ffffffff8123eb79>] validate_chain kernel/locking/lockdep.c:2265 [inline]
 [<ffffffff8123eb79>] __lock_acquire+0x2bf9/0x3640 kernel/locking/lockdep.c:3345
 [<ffffffff8123fffe>] lock_acquire+0x12e/0x410 kernel/locking/lockdep.c:3756
 [<ffffffff838ad6b1>] down_write+0x41/0xa0 kernel/locking/rwsem.c:52
 [<ffffffff8148462f>] inode_lock include/linux/fs.h:746 [inline]
 [<ffffffff8148462f>] shmem_file_llseek+0xef/0x240 mm/shmem.c:2403
 [<ffffffff8156bc22>] vfs_llseek+0xa2/0xd0 fs/read_write.c:301
 [<ffffffff82d49837>] ashmem_llseek+0xe7/0x1f0 drivers/staging/android/ashmem.c:355
 [<ffffffff8156f68b>] vfs_llseek fs/read_write.c:301 [inline]
 [<ffffffff8156f68b>] SYSC_lseek fs/read_write.c:314 [inline]
 [<ffffffff8156f68b>] SyS_lseek+0xeb/0x170 fs/read_write.c:305
 [<ffffffff81006505>] do_syscall_64+0x1a5/0x490 arch/x86/entry/common.c:282
 [<ffffffff838b3e7d>] entry_SYSCALL_64_after_swapgs+0x47/0xc5
audit: type=1400 audit(1518849840.244:13): avc:  denied  { setgid } for  pid=5288 comm="syz-executor0" capability=6  scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=cap_userns permissive=1
keychord: invalid keycode count 0
keychord: invalid keycode count 0
IPVS: Creating netns size=2536 id=9
audit: type=1400 audit(1518849844.274:14): avc:  denied  { create } for  pid=5625 comm="syz-executor3" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1
audit: type=1400 audit(1518849844.304:15): avc:  denied  { write } for  pid=5625 comm="syz-executor3" path="socket:[14879]" dev="sockfs" ino=14879 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1
audit: type=1400 audit(1518849844.304:16): avc:  denied  { getopt } for  pid=5625 comm="syz-executor3" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1
capability: warning: `syz-executor4' uses 32-bit capabilities (legacy support in use)
audit: type=1400 audit(1518849849.414:17): avc:  denied  { create } for  pid=5828 comm="syz-executor5" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_crypto_socket permissive=1
device lo entered promiscuous mode
device eql entered promiscuous mode