bisecting fixing commit since 291009f656e8eaebbdfd3a8d99f6b190a9ce9deb
building syzkaller on a52ee10ae11c1342cfca60cf3957619bcf92bd1a
testing commit 291009f656e8eaebbdfd3a8d99f6b190a9ce9deb with gcc (GCC) 10.2.1 20210217
kernel signature: 1ef186fdf3b441ce865fe65f74af12a41fe3782ad94651aad6f64371cb923f45
all runs: crashed: KASAN: use-after-free Read in v4l2_fh_init
testing current HEAD f296bfd5cd04cbb49b8fc9585adc280ab2b58624
testing commit f296bfd5cd04cbb49b8fc9585adc280ab2b58624 with gcc (GCC) 10.2.1 20210217
kernel signature: 86c33489af710a9c4d8ad79f2484dc13ad8069d62356eb9922e1415c20f81982
all runs: crashed: KASAN: use-after-free Read in v4l2_fh_init
revisions tested: 2, total time: 20m10.244679198s (build: 12m39.647129877s, test: 6m57.321436492s)
the crash still happens on HEAD
commit msg: Merge tag 'nfs-for-5.12-2' of git://git.linux-nfs.org/projects/anna/linux-nfs
crash: KASAN: use-after-free Read in v4l2_fh_init
==================================================================
BUG: KASAN: use-after-free in v4l2_fh_init+0x274/0x2c0 drivers/media/v4l2-core/v4l2-fh.c:25
Read of size 8 at addr ffff8880165148b8 by task v4l_id/10112

CPU: 0 PID: 10112 Comm: v4l_id Not tainted 5.12.0-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:79 [inline]
 dump_stack+0x93/0xc2 lib/dump_stack.c:120
 print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:232
 __kasan_report mm/kasan/report.c:399 [inline]
 kasan_report.cold+0x7c/0xd8 mm/kasan/report.c:416
 v4l2_fh_init+0x274/0x2c0 drivers/media/v4l2-core/v4l2-fh.c:25
 v4l2_fh_open+0x78/0xb0 drivers/media/v4l2-core/v4l2-fh.c:63
 em28xx_v4l2_open+0xd6/0x430 drivers/media/usb/em28xx/em28xx-video.c:2163
 v4l2_open+0x1e3/0x370 drivers/media/v4l2-core/v4l2-dev.c:428
 chrdev_open+0x20f/0x650 fs/char_dev.c:414
 do_dentry_open+0x42a/0xfb0 fs/open.c:826
 do_open fs/namei.c:3365 [inline]
 path_openat+0x9ee/0x22b0 fs/namei.c:3498
 do_filp_open+0x16d/0x390 fs/namei.c:3525
 do_sys_openat2+0x11e/0x360 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_open fs/open.c:1211 [inline]
 __se_sys_open fs/open.c:1207 [inline]
 __x64_sys_open+0xfd/0x1a0 fs/open.c:1207
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fdf48ba9840
Code: 73 01 c3 48 8b 0d 68 77 20 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 89 bb 20 00 00 75 10 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 1e f6 ff ff 48 89 04 24
RSP: 002b:00007ffe9d14e2b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007ffe9d14e428 RCX: 00007fdf48ba9840
RDX: 00007fdf48b95ea0 RSI: 0000000000000000 RDI: 00007ffe9d14ff1f
RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 000055c1339c38d0
R13: 00007ffe9d14e420 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the page:
page:00000000aa5248e2 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x0 pfn:0x16514
flags: 0xfff00000000000()
raw: 00fff00000000000 ffffea000099eb08 ffffea0000ef4c08 0000000000000000
raw: 0000000000000000 0000000000000002 00000000ffffff7f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888016514780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888016514800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888016514880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                        ^
 ffff888016514900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888016514980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================