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SubjectKASAN: use-after-free Read in _free_event

syzbot found the following crash on:

HEAD commit: abf02e29 Merge tag 'pm-5.2-rc6' of git://
git tree: upstream
console output:
kernel config:
dashboard link:
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:

BUG: KASAN: use-after-free in atomic_read
include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: use-after-free in refcount_sub_and_test_checked+0x87/0x200
Read of size 4 at addr ffff88804e9f06e0 by task syz-executor.5/13046

CPU: 1 PID: 13046 Comm: syz-executor.5 Not tainted 5.2.0-rc5+ #38
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
__kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
kasan_report+0x12/0x20 mm/kasan/common.c:614
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x123/0x190 mm/kasan/generic.c:191
kasan_check_read+0x11/0x20 mm/kasan/common.c:94
atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
refcount_sub_and_test_checked+0x87/0x200 lib/refcount.c:182
refcount_dec_and_test_checked+0x1b/0x20 lib/refcount.c:220
put_task_struct include/linux/sched/task.h:98 [inline]
_free_event+0x3d5/0x13a0 kernel/events/core.c:4470
free_event+0x5f/0xd0 kernel/events/core.c:4491
perf_event_release_kernel+0x5b2/0xbe0 kernel/events/core.c:4652
perf_release+0x37/0x50 kernel/events/core.c:4666
__fput+0x2ff/0x890 fs/file_table.c:280
____fput+0x16/0x20 fs/file_table.c:313
task_work_run+0x145/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:185 [inline]
exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:168
prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
do_syscall_64+0x58e/0x680 arch/x86/entry/common.c:304
RIP: 0033:0x412fb1
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 1b 00 00 c3 48
83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48
89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffe25e1b730 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000412fb1
RDX: 0000000000000000 RSI: 0000000000000081 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000760a38 R09: ffffffffffffffff
R10: 00007ffe25e1b800 R11: 0000000000000293 R12: 0000000000760a40
R13: 0000000000000003 R14: 0000000000000001 R15: 000000000075bfd4

Allocated by task 13049:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_kmalloc mm/kasan/common.c:489 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:497
slab_post_alloc_hook mm/slab.h:437 [inline]
slab_alloc_node mm/slab.c:3269 [inline]
kmem_cache_alloc_node+0x131/0x710 mm/slab.c:3579
alloc_task_struct_node kernel/fork.c:160 [inline]
dup_task_struct kernel/fork.c:848 [inline]
copy_process.part.0+0x43f7/0x6790 kernel/fork.c:1868
copy_process kernel/fork.c:1800 [inline]
_do_fork+0x25d/0xfe0 kernel/fork.c:2369
__do_sys_clone kernel/fork.c:2476 [inline]
__se_sys_clone kernel/fork.c:2470 [inline]
__x64_sys_clone+0xbf/0x150 kernel/fork.c:2470
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301

Freed by task 8689:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
__cache_free mm/slab.c:3432 [inline]
kmem_cache_free+0x86/0x260 mm/slab.c:3698
free_task_struct kernel/fork.c:165 [inline]
free_task+0xdd/0x120 kernel/fork.c:460
__delayed_free_task+0x19/0x20 kernel/fork.c:1744
__rcu_reclaim kernel/rcu/rcu.h:222 [inline]
rcu_do_batch kernel/rcu/tree.c:2092 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2310 [inline]
rcu_core+0xba5/0x1500 kernel/rcu/tree.c:2291
__do_softirq+0x25c/0x94c kernel/softirq.c:292

The buggy address belongs to the object at ffff88804e9f06c0
which belongs to the cache task_struct(97:syz5) of size 6080
The buggy address is located 32 bytes inside of
6080-byte region [ffff88804e9f06c0, ffff88804e9f1e80)
The buggy address belongs to the page:
page:ffffea00013a7c00 refcount:1 mapcount:0 mapping:ffff888090b5de40
index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0001681f88 ffffea0001576488 ffff888090b5de40
raw: 0000000000000000 ffff88804e9f06c0 0000000100000001 ffff888058fda540
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88804e9f0580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88804e9f0600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff88804e9f0680: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
ffff88804e9f0700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88804e9f0780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

This bug is generated by a bot. It may contain errors.
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