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BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:840 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xaea/0xcc0 fs/ext4/extents.c:956
Read of size 4 at addr ffff888055a45c94 by task kworker/u4:9/1075

CPU: 0 UID: 0 PID: 1075 Comm: kworker/u4:9 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: writeback wb_workfn (flush-7:0)
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 ext4_ext_binsearch fs/ext4/extents.c:840 [inline]
 ext4_find_extent+0xaea/0xcc0 fs/ext4/extents.c:956
 ext4_ext_map_blocks+0x283/0x58b0 fs/ext4/extents.c:4261
 ext4_map_create_blocks+0x11d/0x540 fs/ext4/inode.c:616
 ext4_map_blocks+0x7cd/0x11d0 fs/ext4/inode.c:809
 mpage_map_one_extent fs/ext4/inode.c:2373 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2467 [inline]
 ext4_do_writepages+0x22c0/0x46e0 fs/ext4/inode.c:2925
 ext4_writepages+0x241/0x3b0 fs/ext4/inode.c:3019
 do_writepages+0x32e/0x550 mm/page-writeback.c:2554
 __writeback_single_inode+0x133/0x11a0 fs/fs-writeback.c:1750
 writeback_sb_inodes+0x992/0x1a20 fs/fs-writeback.c:2042
 wb_writeback+0x456/0xb70 fs/fs-writeback.c:2227
 wb_do_writeback fs/fs-writeback.c:2374 [inline]
 wb_workfn+0x414/0xf50 fs/fs-writeback.c:2414
 process_one_work kernel/workqueue.c:3275 [inline]
 process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
 worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
 kthread+0x388/0x470 kernel/kthread.c:467
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888000000000 pfn:0x55a45
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
raw: 04fff00000000000 ffffea0001569108 ffffea0001483248 0000000000000000
raw: ffff888000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x440dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_COMP), pid 5433, tgid 5433 (syz-executor), ts 119865096298, free_ts 120597011404
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2484
 alloc_frozen_pages_noprof mm/mempolicy.c:2555 [inline]
 alloc_pages_noprof+0xa8/0x190 mm/mempolicy.c:2575
 pagetable_alloc_noprof include/linux/mm.h:3404 [inline]
 pmd_alloc_one_noprof include/asm-generic/pgalloc.h:143 [inline]
 __pmd_alloc+0x3a/0x860 mm/memory.c:6709
 pmd_alloc include/linux/mm.h:3320 [inline]
 copy_pmd_range+0x7c1c/0x8050 mm/memory.c:1385
 copy_pud_range mm/memory.c:1442 [inline]
 copy_p4d_range mm/memory.c:1466 [inline]
 copy_page_range+0xbe8/0x11f0 mm/memory.c:1552
 dup_mmap+0xf40/0x1d90 mm/mmap.c:1841
 dup_mm kernel/fork.c:1530 [inline]
 copy_mm+0x13b/0x4b0 kernel/fork.c:1582
 copy_process+0x18b6/0x3cf0 kernel/fork.c:2223
 kernel_clone+0x248/0x8e0 kernel/fork.c:2654
 __do_sys_clone kernel/fork.c:2795 [inline]
 __se_sys_clone kernel/fork.c:2779 [inline]
 __x64_sys_clone+0x1b6/0x230 kernel/fork.c:2779
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 15 tgid 15 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 __tlb_remove_table_free mm/mmu_gather.c:228 [inline]
 tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:291
 rcu_do_batch kernel/rcu/tree.c:2617 [inline]
 rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
 handle_softirqs+0x22a/0x870 kernel/softirq.c:622
 run_ksoftirqd+0x36/0x60 kernel/softirq.c:1063
 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
 kthread+0x388/0x470 kernel/kthread.c:467
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888055a45b80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888055a45c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888055a45c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                         ^
 ffff888055a45d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888055a45d80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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