Hello, syzbot found the following issue on: HEAD commit: 15ac8fdb Add linux-next specific files for 20201207 git tree: linux-next console output: https://syzkaller.appspot.com/x/log.txt?x=1735927b500000 kernel config: https://syzkaller.appspot.com/x/.config?x=3696b8138207d24d dashboard link: https://syzkaller.appspot.com/bug?extid=aded2f2ab94d81727898 compiler: gcc (GCC) 10.1.0-syz 20200507 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11993623500000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15799413500000 The issue was bisected to: commit 4d004099a668c41522242aa146a38cc4eb59cb1e Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Date: Fri Oct 2 09:04:21 2020 +0000 lockdep: Fix lockdep recursion bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1469d00f500000 final oops: https://syzkaller.appspot.com/x/report.txt?x=1669d00f500000 console output: https://syzkaller.appspot.com/x/log.txt?x=1269d00f500000 IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+aded2f2ab94d81727898@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes: 4d004099a668 ("lockdep: Fix lockdep recursion") ================================================================== BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:101 [inline] BUG: KASAN: null-ptr-deref in atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline] BUG: KASAN: null-ptr-deref in __refcount_sub_and_test include/linux/refcount.h:272 [inline] BUG: KASAN: null-ptr-deref in __refcount_dec_and_test include/linux/refcount.h:315 [inline] BUG: KASAN: null-ptr-deref in refcount_dec_and_test include/linux/refcount.h:333 [inline] BUG: KASAN: null-ptr-deref in kref_put include/linux/kref.h:64 [inline] BUG: KASAN: null-ptr-deref in bdi_put+0x22/0xa0 mm/backing-dev.c:901 Write of size 4 at addr 0000000000000040 by task syz-executor719/8459 CPU: 1 PID: 8459 Comm: syz-executor719 Not tainted 5.10.0-rc6-next-20201207-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:79 [inline] dump_stack+0x107/0x163 lib/dump_stack.c:120 __kasan_report mm/kasan/report.c:400 [inline] kasan_report.cold+0x5f/0xd5 mm/kasan/report.c:413 check_memory_region_inline mm/kasan/generic.c:180 [inline] check_memory_region+0x13d/0x180 mm/kasan/generic.c:186 instrument_atomic_read_write include/linux/instrumented.h:101 [inline] atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline] __refcount_sub_and_test include/linux/refcount.h:272 [inline] __refcount_dec_and_test include/linux/refcount.h:315 [inline] refcount_dec_and_test include/linux/refcount.h:333 [inline] kref_put include/linux/kref.h:64 [inline] bdi_put+0x22/0xa0 mm/backing-dev.c:901 bdev_evict_inode+0x280/0x4a0 fs/block_dev.c:809 evict+0x2ed/0x6b0 fs/inode.c:577 iput_final fs/inode.c:1651 [inline] iput.part.0+0x41e/0x840 fs/inode.c:1677 iput+0x58/0x70 fs/inode.c:1667 dentry_unlink_inode+0x2b1/0x3d0 fs/dcache.c:374 __dentry_kill+0x3c0/0x640 fs/dcache.c:579 dentry_kill fs/dcache.c:705 [inline] dput+0x786/0xc10 fs/dcache.c:878 do_one_tree fs/dcache.c:1625 [inline] shrink_dcache_for_umount+0x11f/0x330 fs/dcache.c:1639 generic_shutdown_super+0x68/0x370 fs/super.c:447 kill_anon_super+0x36/0x60 fs/super.c:1055 deactivate_locked_super+0x94/0x160 fs/super.c:335 deactivate_super+0xad/0xd0 fs/super.c:366 cleanup_mnt+0x3a3/0x530 fs/namespace.c:1123 task_work_run+0xdd/0x190 kernel/task_work.c:140 tracehook_notify_resume include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop kernel/entry/common.c:174 [inline] exit_to_user_mode_prepare+0x1f0/0x200 kernel/entry/common.c:201 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline] syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:302 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x444439 Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 0f 83 db d7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007ffc4e2a8a38 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 RAX: ffffffffffffffea RBX: 00007ffc4e2a8a40 RCX: 0000000000444439 RDX: 0000000020000100 RSI: 00000000200000c0 RDI: 0000000000000000 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000400c60 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004020a0 R13: 0000000000402130 R14: 0000000000000000 R15: 0000000000000000 ================================================================== --- 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
