Hello, syzbot hit the following crash on upstream commit c89be5242607d8aa08a6fa45a887c68b2d4a2a2c (Sun Feb 25 21:43:18 2018 +0000) Merge tag 'nfs-for-4.16-3' of git://git.linux-nfs.org/projects/trondmy/linux-nfs So far this crash happened 1820 times on upstream. C reproducer is attached. syzkaller reproducer is attached. Raw console output is attached. compiler: gcc (GCC) 7.1.1 20170620 .config is attached. IMPORTANT: if you fix the bug, please add the following tag to the commit: Reported-by: syzbot+d7a918a7a8e1c952bc36@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(1519638766.030:7): avc: denied { map } for pid=4243 comm="syzkaller923784" path="/root/syzkaller923784171" dev="sda1" ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1 audit: type=1400 audit(1519638766.030:8): avc: denied { map } for pid=4243 comm="syzkaller923784" path="/dev/ashmem" dev="devtmpfs" ino=9417 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 4.16.0-rc2+ #329 Not tainted ------------------------------------------------------ syzkaller923784/4243 is trying to acquire lock: (&mm->mmap_sem){++++}, at: [<0000000074c86253>] __might_fault+0xe0/0x1d0 mm/memory.c:4570 but task is already holding lock: (ashmem_mutex){+.+.}, at: [<0000000024db7f7c>] ashmem_pin_unpin drivers/staging/android/ashmem.c:705 [inline] (ashmem_mutex){+.+.}, at: [<0000000024db7f7c>] ashmem_ioctl+0x3db/0x11b0 drivers/staging/android/ashmem.c:782 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (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:362 call_mmap include/linux/fs.h:1786 [inline] mmap_region+0xa99/0x15a0 mm/mmap.c:1705 do_mmap+0x6c0/0xe00 mm/mmap.c:1483 do_mmap_pgoff include/linux/mm.h:2223 [inline] vm_mmap_pgoff+0x1de/0x280 mm/util.c:355 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 do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7 -> #0 (&mm->mmap_sem){++++}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920 __might_fault+0x13a/0x1d0 mm/memory.c:4571 _copy_from_user+0x2c/0x110 lib/usercopy.c:10 copy_from_user include/linux/uaccess.h:147 [inline] ashmem_pin_unpin drivers/staging/android/ashmem.c:710 [inline] ashmem_ioctl+0x438/0x11b0 drivers/staging/android/ashmem.c:782 vfs_ioctl fs/ioctl.c:46 [inline] do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692 do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(ashmem_mutex); lock(&mm->mmap_sem); lock(ashmem_mutex); lock(&mm->mmap_sem); *** DEADLOCK *** 1 lock held by syzkaller923784/4243: #0: (ashmem_mutex){+.+.}, at: [<0000000024db7f7c>] ashmem_pin_unpin drivers/staging/android/ashmem.c:705 [inline] #0: (ashmem_mutex){+.+.}, at: [<0000000024db7f7c>] ashmem_ioctl+0x3db/0x11b0 drivers/staging/android/ashmem.c:782 stack backtrace: CPU: 1 PID: 4243 Comm: syzkaller923784 Not tainted 4.16.0-rc2+ #329 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+0x194/0x24d lib/dump_stack.c:53 print_circular_bug.isra.38+0x2cd/0x2dc kernel/locking/lockdep.c:1223 check_prev_add kernel/locking/lockdep.c:1863 [inline] check_prevs_add kernel/locking/lockdep.c:1976 [inline] validate_chain kernel/locking/lockdep.c:2417 [inline] __lock_acquire+0x30a8/0x3e00 kernel/locking/lockdep.c:3431 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920 __might_fault+0x13a/0x1d0 mm/memory.c:4571 _copy_from_user+0x2c/0x110 lib/usercopy.c:10 copy_from_user include/linux/uaccess.h:147 [inline] ashmem_pin_unpin drivers/staging/android/ashmem.c:710 [inline] ashmem_ioctl+0x438/0x11b0 drivers/staging/android/ashmem.c:782 vfs_ioctl fs/ioctl.c:46 [inline] do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692 do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7 RIP: 0033:0x43fd19 RSP: 002b:00007ffe04d2fda8 EFLAGS: 00000217 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fd19 RDX: 0000000000000000 RSI: 0000000000007709 RDI: 0000000000000003 RBP: 000000 --- This bug is generated by a dumb bot. 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