====================================================== [ 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: [] shmem_file_llseek+0xf1/0x240 mm/shmem.c:1816 but task is already holding lock: (ashmem_mutex){+.+.+.}, at: [] 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: [] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592 [] __mutex_lock_common kernel/locking/mutex.c:521 [inline] [] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621 [] ashmem_mmap+0x53/0x400 drivers/staging/android/ashmem.c:366 [] mmap_region+0x94f/0x1250 mm/mmap.c:1664 [] do_mmap+0x4fd/0x9d0 mm/mmap.c:1441 [] do_mmap_pgoff include/linux/mm.h:1915 [inline] [] vm_mmap_pgoff+0x16e/0x1c0 mm/util.c:272 [] SYSC_mmap_pgoff mm/mmap.c:1491 [inline] [] SyS_mmap_pgoff+0x33f/0x560 mm/mmap.c:1449 [] SYSC_mmap arch/x86/kernel/sys_x86_64.c:95 [inline] [] SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:86 [] entry_SYSCALL_64_fastpath+0x16/0x92 [] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592 [] __might_fault+0x14a/0x1d0 mm/memory.c:3810 [] copy_to_user arch/x86/include/asm/uaccess.h:760 [inline] [] filldir+0x162/0x2d0 fs/readdir.c:180 [] dir_emit_dot include/linux/fs.h:3068 [inline] [] dir_emit_dots include/linux/fs.h:3079 [inline] [] dcache_readdir+0x11e/0x7b0 fs/libfs.c:150 [] iterate_dir+0x1c8/0x420 fs/readdir.c:42 [] SYSC_getdents fs/readdir.c:215 [inline] [] SyS_getdents+0x14a/0x270 fs/readdir.c:196 [] entry_SYSCALL_64_fastpath+0x16/0x92 [] check_prev_add kernel/locking/lockdep.c:1853 [inline] [] check_prevs_add kernel/locking/lockdep.c:1958 [inline] [] validate_chain kernel/locking/lockdep.c:2144 [inline] [] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213 [] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592 [] __mutex_lock_common kernel/locking/mutex.c:521 [inline] [] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621 [] shmem_file_llseek+0xf1/0x240 mm/shmem.c:1816 [] vfs_llseek+0xa2/0xd0 fs/read_write.c:260 [] ashmem_llseek+0xe7/0x1f0 drivers/staging/android/ashmem.c:342 [] vfs_llseek fs/read_write.c:260 [inline] [] SYSC_lseek fs/read_write.c:285 [inline] [] SyS_lseek+0xeb/0x170 fs/read_write.c:276 [] 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: [] 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: [] __dump_stack lib/dump_stack.c:15 [inline] [] dump_stack+0xc1/0x124 lib/dump_stack.c:51 [] print_circular_bug+0x271/0x310 kernel/locking/lockdep.c:1226 [] check_prev_add kernel/locking/lockdep.c:1853 [inline] [] check_prevs_add kernel/locking/lockdep.c:1958 [inline] [] validate_chain kernel/locking/lockdep.c:2144 [inline] [] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213 [] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592 [] __mutex_lock_common kernel/locking/mutex.c:521 [inline] [] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621