Hello, syzbot found the following issue on: HEAD commit: 8cae8cd89f05 seq_file: disallow extremely large seq buffer.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=1083e8cc300000 kernel config: https://syzkaller.appspot.com/x/.config?x=7273c75708b55890 dashboard link: https://syzkaller.appspot.com/bug?extid=579885d1a9a833336209 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=163905f2300000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=165bd0ea300000 The issue was bisected to: commit 82a763e61e2b601309d696d4fa514c77d64ee1be Author: Miklos Szeredi <mszeredi@xxxxxxxxxx> Date: Mon Dec 14 14:26:14 2020 +0000 ovl: simplify file splice bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13440c82300000 final oops: https://syzkaller.appspot.com/x/report.txt?x=10c40c82300000 console output: https://syzkaller.appspot.com/x/log.txt?x=17440c82300000 IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+579885d1a9a833336209@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes: 82a763e61e2b ("ovl: simplify file splice") ====================================================== WARNING: possible circular locking dependency detected 5.14.0-rc2-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor005/9173 is trying to acquire lock: ffff888027e98468 (&pipe->mutex/1){+.+.}-{3:3}, at: pipe_lock_nested fs/pipe.c:66 [inline] ffff888027e98468 (&pipe->mutex/1){+.+.}-{3:3}, at: pipe_lock+0x5a/0x70 fs/pipe.c:74 but task is already holding lock: ffff888147cfc460 (sb_writers#5){.+.+}-{0:0}, at: __do_splice+0x134/0x250 fs/splice.c:1144 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (sb_writers#5){.+.+}-{0:0}: percpu_down_read include/linux/percpu-rwsem.h:51 [inline] __sb_start_write include/linux/fs.h:1763 [inline] sb_start_write include/linux/fs.h:1833 [inline] file_start_write include/linux/fs.h:3040 [inline] ovl_write_iter+0x1015/0x17f0 fs/overlayfs/file.c:357 call_write_iter include/linux/fs.h:2114 [inline] do_iter_readv_writev+0x46f/0x740 fs/read_write.c:740 do_iter_write+0x188/0x670 fs/read_write.c:866 vfs_iter_write+0x70/0xa0 fs/read_write.c:907 iter_file_splice_write+0x723/0xc70 fs/splice.c:689 do_splice_from fs/splice.c:767 [inline] do_splice+0xb7e/0x1960 fs/splice.c:1079 __do_splice+0x134/0x250 fs/splice.c:1144 __do_sys_splice fs/splice.c:1350 [inline] __se_sys_splice fs/splice.c:1332 [inline] __x64_sys_splice+0x198/0x250 fs/splice.c:1332 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #1 (&ovl_i_mutex_key[depth]){+.+.}-{3:3}: down_write+0x92/0x150 kernel/locking/rwsem.c:1406 inode_lock include/linux/fs.h:774 [inline] ovl_write_iter+0x17d/0x17f0 fs/overlayfs/file.c:341 call_write_iter include/linux/fs.h:2114 [inline] do_iter_readv_writev+0x46f/0x740 fs/read_write.c:740 do_iter_write+0x188/0x670 fs/read_write.c:866 vfs_iter_write+0x70/0xa0 fs/read_write.c:907 iter_file_splice_write+0x723/0xc70 fs/splice.c:689 do_splice_from fs/splice.c:767 [inline] do_splice+0xb7e/0x1960 fs/splice.c:1079 __do_splice+0x134/0x250 fs/splice.c:1144 __do_sys_splice fs/splice.c:1350 [inline] __se_sys_splice fs/splice.c:1332 [inline] __x64_sys_splice+0x198/0x250 fs/splice.c:1332 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #0 (&pipe->mutex/1){+.+.}-{3:3}: check_prev_add kernel/locking/lockdep.c:3051 [inline] check_prevs_add kernel/locking/lockdep.c:3174 [inline] validate_chain kernel/locking/lockdep.c:3789 [inline] __lock_acquire+0x2a07/0x54a0 kernel/locking/lockdep.c:5015 lock_acquire kernel/locking/lockdep.c:5625 [inline] lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590 __mutex_lock_common kernel/locking/mutex.c:959 [inline] __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104 pipe_lock_nested fs/pipe.c:66 [inline] pipe_lock+0x5a/0x70 fs/pipe.c:74 iter_file_splice_write+0x183/0xc70 fs/splice.c:635 do_splice_from fs/splice.c:767 [inline] do_splice+0xb7e/0x1960 fs/splice.c:1079 __do_splice+0x134/0x250 fs/splice.c:1144 __do_sys_splice fs/splice.c:1350 [inline] __se_sys_splice fs/splice.c:1332 [inline] __x64_sys_splice+0x198/0x250 fs/splice.c:1332 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Chain exists of: &pipe->mutex/1 --> &ovl_i_mutex_key[depth] --> sb_writers#5 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(sb_writers#5); lock(&ovl_i_mutex_key[depth]); lock(sb_writers#5); lock(&pipe->mutex/1); *** DEADLOCK *** 1 lock held by syz-executor005/9173: #0: ffff888147cfc460 (sb_writers#5){.+.+}-{0:0}, at: __do_splice+0x134/0x250 fs/splice.c:1144 stack backtrace: CPU: 0 PID: 9173 Comm: syz-executor005 Not tainted 5.14.0-rc2-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2131 check_prev_add kernel/locking/lockdep.c:3051 [inline] check_prevs_add kernel/locking/lockdep.c:3174 [inline] validate_chain kernel/locking/lockdep.c:3789 [inline] __lock_acquire+0x2a07/0x54a0 kernel/locking/lockdep.c:5015 lock_acquire kernel/locking/lockdep.c:5625 [inline] lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590 __mutex_lock_common kernel/locking/mutex.c:959 [inline] __mutex_lock+0x12a/0x10a0 kernel/locking/mutex.c:1104 pipe_lock_nested fs/pipe.c:66 [inline] pipe_lock+0x5a/0x70 fs/pipe.c:74 iter_file_splice_write+0x183/0xc70 fs/splice.c:635 do_splice_from fs/splice.c:767 [inline] do_splice+0xb7e/0x1960 fs/splice.c:1079 __do_splice+0x134/0x250 fs/splice.c:1144 __do_sys_splice fs/splice.c:1350 [inline] __se_sys_splice fs/splice.c:1332 [inline] __x64_sys_splice+0x198/0x250 fs/splice.c:1332 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x446219 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f1d5746e2e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000113 RAX: ffffffffffffffda RBX: 00000000004cb4e0 RCX: 0000000000446219 RDX: 0000000000000006 RSI: 0000000000000000 RDI: 0000000000000004 RBP: 000000000049b06c R08: 000000000004ffdc R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 3d72696472657070 R13: 0079616c7265766f R14: 69662f7375622f2e R15: 00000000004cb4e8 --- This report is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. syzbot will keep track of this issue. See: https://goo.gl/tpsmEJ#status for how to communicate with syzbot. For information about bisection process see: https://goo.gl/tpsmEJ#bisection syzbot can test patches for this issue, for details see: https://goo.gl/tpsmEJ#testing-patches
