bisecting fixing commit since 4d41ead6ead97c3730bbd186a601a64828668f01
building syzkaller on d5a3ae1f760e7cb2cd5a721d9645ae22eae114fe
testing commit 4d41ead6ead97c3730bbd186a601a64828668f01 with gcc (GCC) 8.1.0
kernel signature: bb714c443741911cf75e8ed5acfcc03071a7e4cc4fabc8b83b7753e7f4302d12
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in fq_codel_enqueue
testing current HEAD c2e7554e1b85935d962127efa3c2a76483b0b3b6
testing commit c2e7554e1b85935d962127efa3c2a76483b0b3b6 with gcc (GCC) 8.1.0
kernel signature: 8fa99cfb04540c951133586fe355cc7208245151716960d4b2899c67f4ee4b59
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in fq_codel_enqueue
revisions tested: 2, total time: 15m24.877255343s (build: 9m23.853476032s, test: 5m24.769931621s)
the crash still happens on HEAD
commit msg: Merge tag 'gfs2-v5.10-rc4-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2
crash: BUG: unable to handle kernel NULL pointer dereference in fq_codel_enqueue
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 11e21b067 P4D 11e21b067 PUD 11e21c067 PMD 0 
Oops: 0000 [#1] PREEMPT SMP
CPU: 1 PID: 8348 Comm: syz-executor.4 Not tainted 5.10.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:dequeue_head net/sched/sch_fq_codel.c:120 [inline]
RIP: 0010:fq_codel_drop net/sched/sch_fq_codel.c:168 [inline]
RIP: 0010:fq_codel_enqueue+0x28b/0x3f0 net/sched/sch_fq_codel.c:230
Code: 48 c1 e7 06 48 89 44 24 10 48 03 bb d0 02 00 00 45 31 ed 45 31 c0 31 c9 89 74 24 20 eb 06 3b 54 24 28 73 36 48 8b 07 83 c1 01 <48> 8b 10 48 89 17 8b 50 28 44 8b 58 34 48 c7 00 00 00 00 00 49 8b
RSP: 0018:ffffc90002a27ab0 EFLAGS: 00010202
RAX: 0000000000000000 RBX: ffff88811dc12000 RCX: 0000000000000001
RDX: 0000000000000400 RSI: 0000000000000001 RDI: ffff88811e340000
RBP: ffffc90002a27b30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000300 R11: 0000000000000003 R12: ffffc90002a27b60
R13: 0000000000000000 R14: 0000000000000040 R15: 0000000002000000
FS:  00007fd143d5f700(0000) GS:ffff88813bd00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000011e214000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __dev_xmit_skb net/core/dev.c:3797 [inline]
 __dev_queue_xmit+0x67a/0xd20 net/core/dev.c:4108
 __netlink_deliver_tap_skb net/netlink/af_netlink.c:295 [inline]
 __netlink_deliver_tap net/netlink/af_netlink.c:313 [inline]
 netlink_deliver_tap+0x374/0x3d0 net/netlink/af_netlink.c:326
 netlink_deliver_tap_kernel net/netlink/af_netlink.c:335 [inline]
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x189/0x270 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x248/0x480 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0x2b/0x40 net/socket.c:671
 ____sys_sendmsg+0x1ed/0x230 net/socket.c:2353
 ___sys_sendmsg+0x77/0xb0 net/socket.c:2407
 __sys_sendmsg+0x52/0xa0 net/socket.c:2440
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d5b9
Code: 5d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fd143d5ec78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000002a1c0 RCX: 000000000045d5b9
RDX: 0000000000000000 RSI: 00000000200001c0 RDI: 0000000000000003
RBP: 000000000118cf80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007ffc09d5a7cf R14: 00007fd143d5f9c0 R15: 000000000118cf4c
Modules linked in:
CR2: 0000000000000000
---[ end trace 2e566d95c42d0365 ]---
RIP: 0010:dequeue_head net/sched/sch_fq_codel.c:120 [inline]
RIP: 0010:fq_codel_drop net/sched/sch_fq_codel.c:168 [inline]
RIP: 0010:fq_codel_enqueue+0x28b/0x3f0 net/sched/sch_fq_codel.c:230
Code: 48 c1 e7 06 48 89 44 24 10 48 03 bb d0 02 00 00 45 31 ed 45 31 c0 31 c9 89 74 24 20 eb 06 3b 54 24 28 73 36 48 8b 07 83 c1 01 <48> 8b 10 48 89 17 8b 50 28 44 8b 58 34 48 c7 00 00 00 00 00 49 8b
RSP: 0018:ffffc90002a27ab0 EFLAGS: 00010202
RAX: 0000000000000000 RBX: ffff88811dc12000 RCX: 0000000000000001
RDX: 0000000000000400 RSI: 0000000000000001 RDI: ffff88811e340000
RBP: ffffc90002a27b30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000300 R11: 0000000000000003 R12: ffffc90002a27b60
R13: 0000000000000000 R14: 0000000000000040 R15: 0000000002000000
FS:  00007fd143d5f700(0000) GS:ffff88813bd00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000011e214000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400