Hello, syzkaller hit the following crash on d476c5334f1dee122534b29639f8d46a85ecbb9d git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master compiler: gcc (GCC) 7.1.1 20170620 .config is attached Raw console output is attached. C reproducer is attached syzkaller reproducer is attached. See https://goo.gl/kgGztJ for information about syzkaller reproducers IMPORTANT: if you fix the bug, please add the following tag to the commit: Reported-by: syzbot+8ec30bb7bf1a981a2012@syzkaller.appspotmail.com It will help syzbot understand when the bug is fixed. See footer for details. If you forward the report, please keep this part and the footer. ====================================================== audit: type=1400 audit(1515535006.781:8): avc: denied { map } for pid=3497 comm="syzkaller303685" path="/dev/ashmem" dev="devtmpfs" ino=178 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=system_u:object_r:device_t:s0 tclass=chr_file permissive=1 WARNING: possible circular locking dependency detected 4.15.0-rc7+ #255 Not tainted ------------------------------------------------------ syzkaller303685/3497 is trying to acquire lock: (&sb->s_type->i_mutex_key#11){++++}, at: [<000000006886b3fb>] inode_lock include/linux/fs.h:713 [inline] (&sb->s_type->i_mutex_key#11){++++}, at: [<000000006886b3fb>] shmem_file_llseek+0xef/0x240 mm/shmem.c:2579 but task is already holding lock: (ashmem_mutex){+.+.}, at: [<00000000a44304a8>] ashmem_llseek+0x56/0x1f0 drivers/staging/android/ashmem.c:334 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:756 [inline] __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 ashmem_mmap+0x53/0x410 drivers/staging/android/ashmem.c:370 call_mmap include/linux/fs.h:1777 [inline] mmap_region+0xa99/0x15a0 mm/mmap.c:1705 do_mmap+0x6c0/0xe00 mm/mmap.c:1483 do_mmap_pgoff include/linux/mm.h:2217 [inline] vm_mmap_pgoff+0x1de/0x280 mm/util.c:333 SYSC_mmap_pgoff mm/mmap.c:1533 [inline] SyS_mmap_pgoff+0x462/0x5f0 mm/mmap.c:1491 SYSC_mmap arch/x86/kernel/sys_x86_64.c:100 [inline] SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:91 entry_SYSCALL_64_fastpath+0x23/0x9a -> #1 (&mm->mmap_sem){++++}: __might_fault+0x13a/0x1d0 mm/memory.c:4529 _copy_to_user+0x2c/0xc0 lib/usercopy.c:25 copy_to_user include/linux/uaccess.h:155 [inline] filldir+0x1a7/0x320 fs/readdir.c:196 dir_emit_dot include/linux/fs.h:3374 [inline] dir_emit_dots include/linux/fs.h:3385 [inline] dcache_readdir+0x12d/0x5e0 fs/libfs.c:192 iterate_dir+0x1ca/0x530 fs/readdir.c:51 SYSC_getdents fs/readdir.c:231 [inline] SyS_getdents+0x225/0x450 fs/readdir.c:212 entry_SYSCALL_64_fastpath+0x23/0x9a -> #0 (&sb->s_type->i_mutex_key#11){++++}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3914 down_write+0x87/0x120 kernel/locking/rwsem.c:70 inode_lock include/linux/fs.h:713 [inline] shmem_file_llseek+0xef/0x240 mm/shmem.c:2579 vfs_llseek+0xa2/0xd0 fs/read_write.c:300 ashmem_llseek+0xe7/0x1f0 drivers/staging/android/ashmem.c:346 vfs_llseek fs/read_write.c:300 [inline] SYSC_lseek fs/read_write.c:313 [inline] SyS_lseek+0xeb/0x170 fs/read_write.c:304 entry_SYSCALL_64_fastpath+0x23/0x9a other info that might help us debug this: Chain exists of: &sb->s_type->i_mutex_key#11 --> &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#11); *** DEADLOCK *** 1 lock held by syzkaller303685/3497: #0: (ashmem_mutex){+.+.}, at: [<00000000a44304a8>] ashmem_llseek+0x56/0x1f0 drivers/staging/android/ashmem.c:334 stack backtrace: CPU: 0 PID: 3497 Comm: syzkaller303685 Not tainted 4.15.0-rc7+ #255 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:53 print_circular_bug.isra.37+0x2cd/0x2dc kernel/locking/lockdep.c:1218 check_prev_add kernel/locking/lockdep.c:1858 [inline] check_prevs_add kernel/locking/lockdep.c:1971 [inline] validate_chain kernel/locking/lockdep.c:2412 [inline] __lock_acquire+0x30a8/0x3e00 kernel/locking/lockdep.c:3426 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3914 down_write+0x87/0x120 kernel/locking/rwsem.c:70 inode_lock include/linux/fs.h:713 [inline] shmem_file_llseek+0xef/0x240 mm/shmem.c:2579 vfs_llseek+0xa2/0xd0 fs/read_write.c:300 ashmem_llseek+0xe7/0x1f0 drivers/staging/android/ashmem.c:346 vfs_llseek fs/read_write.c:300 [inline] SYSC_lseek fs/read_write.c:313 [inline] SyS_lseek+0xeb/0x170 fs/read_write.c:304 entry_SYSCALL_64_fastpath+0x23/0x9a RIP: 0033:0x444aa9 RSP: 002b:00007ffd2bec96f8 EFLAGS: 00000217 ORIG_RAX: 0000000000000008 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000444aa9 RDX: 0000000000000003 RSI: fffffffffffffffc RDI: 0000000000000004 RBP: 00000000 --- This bug is generated by a dumb bot. 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