WARNING: refcount bug in drm_gem_mmap

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a5541c0811a0 Merge branch 'for-next/core' into for-kernelci
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=17329dbc480000
kernel config: https://syzkaller.appspot.com/x/.config?x=cbd4e584773e9397
dashboard link: https://syzkaller.appspot.com/bug?extid=6a18ff929bb82f971e59
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64
CC: [air...@gmail.com christia...@amd.com dan...@ffwll.ch dri-...@lists.freedesktop.org linaro...@lists.linaro.org linux-...@vger.kernel.org linux...@vger.kernel.org maarten....@linux.intel.com mri...@kernel.org sumit....@linaro.org tzimm...@suse.de]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4b7702208fb9/disk-a5541c08.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9ec0153ec051/vmlinux-a5541c08.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6f8725ad290a/Image-a5541c08.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6a18ff...@syzkaller.appspotmail.com

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refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 2862 at lib/refcount.c:28 refcount_warn_saturate+0x1a0/0x1c8 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 2862 Comm: syz-executor.0 Not tainted 6.1.0-rc8-syzkaller-33330-ga5541c0811a0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : refcount_warn_saturate+0x1a0/0x1c8 lib/refcount.c:28
lr : refcount_warn_saturate+0x1a0/0x1c8 lib/refcount.c:28
sp : ffff800012f5ba90
x29: ffff800012f5ba90 x28: ffff00012fac2800 x27: 0000000020ffffff
x26: 0000000021000000 x25: 0000000000000003 x24: 0000000000000001
x23: ffff00011d7a1800 x22: ffff00011d7a1818 x21: ffff0000c4135000
x20: 0000000000000003 x19: ffff80000d95e000 x18: 00000000000000c0
x17: ffff80000dda8198 x16: ffff80000dbe6158 x15: ffff0001228c0000
x14: 0000000000000000 x13: 00000000ffffffff x12: 0000000000040000
x11: 000000000003ffff x10: ffff8000133af000 x9 : 280cee47bda86400
x8 : 280cee47bda86400 x7 : ffff80000c091ebc x6 : 0000000000000000
x5 : 0000000000000080 x4 : 0000000000000001 x3 : 0000000000000000
x2 : 0000000000000000 x1 : 0000000100000000 x0 : 0000000000000026
Call trace:
refcount_warn_saturate+0x1a0/0x1c8 lib/refcount.c:28
__refcount_sub_and_test include/linux/refcount.h:283 [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]
__drm_gem_object_put include/drm/drm_gem.h:430 [inline]
drm_gem_object_put include/drm/drm_gem.h:443 [inline]
drm_gem_mmap+0x30c/0x37c drivers/gpu/drm/drm_gem.c:1121
call_mmap include/linux/fs.h:2204 [inline]
mmap_region+0x8a0/0x1064 mm/mmap.c:2622
do_mmap+0x6e0/0xa28 mm/mmap.c:1412
vm_mmap_pgoff+0xe8/0x1d0 mm/util.c:520
ksys_mmap_pgoff+0x1cc/0x278 mm/mmap.c:1458
__do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
__se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
__arm64_sys_mmap+0x58/0x6c arch/arm64/kernel/sys.c:21
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x140 arch/arm64/kernel/syscall.c:197
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584
irq event stamp: 942596
hardirqs last enabled at (942595): [<ffff8000081c3048>] __up_console_sem+0xb0/0xfc kernel/printk/printk.c:261
hardirqs last disabled at (942596): [<ffff80000c084084>] el1_dbg+0x24/0x80 arch/arm64/kernel/entry-common.c:405
softirqs last enabled at (941912): [<ffff8000080102e4>] _stext+0x2e4/0x37c
softirqs last disabled at (941905): [<ffff800008017c88>] ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:80
---[ end trace 0000000000000000 ]---


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.