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    SubjectRe: [syzbot] possible deadlock in io_sq_thread_finish
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    Hello,

    syzbot has tested the proposed patch but the reproducer is still triggering an issue:
    KASAN: use-after-free Read in io_sq_thread

    ==================================================================
    BUG: KASAN: use-after-free in __lock_acquire+0x3e6f/0x54c0 kernel/locking/lockdep.c:4770
    Read of size 8 at addr ffff88801d418c78 by task iou-sqp-10269/10271

    CPU: 1 PID: 10271 Comm: iou-sqp-10269 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+0x141/0x1d7 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
    __lock_acquire+0x3e6f/0x54c0 kernel/locking/lockdep.c:4770
    lock_acquire kernel/locking/lockdep.c:5510 [inline]
    lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5475
    down_write+0x92/0x150 kernel/locking/rwsem.c:1406
    io_sq_thread+0x1220/0x1b10 fs/io_uring.c:6754
    ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

    Allocated by task 10269:
    kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
    kasan_set_track mm/kasan/common.c:46 [inline]
    set_alloc_info mm/kasan/common.c:427 [inline]
    ____kasan_kmalloc mm/kasan/common.c:506 [inline]
    ____kasan_kmalloc mm/kasan/common.c:465 [inline]
    __kasan_kmalloc+0x99/0xc0 mm/kasan/common.c:515
    kmalloc include/linux/slab.h:554 [inline]
    kzalloc include/linux/slab.h:684 [inline]
    io_get_sq_data fs/io_uring.c:7153 [inline]
    io_sq_offload_create fs/io_uring.c:7827 [inline]
    io_uring_create fs/io_uring.c:9443 [inline]
    io_uring_setup+0x154b/0x2940 fs/io_uring.c:9523
    do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
    entry_SYSCALL_64_after_hwframe+0x44/0xae

    Freed by task 9:
    kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
    kasan_set_track+0x1c/0x30 mm/kasan/common.c:46
    kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:357
    ____kasan_slab_free mm/kasan/common.c:360 [inline]
    ____kasan_slab_free mm/kasan/common.c:325 [inline]
    __kasan_slab_free+0xf5/0x130 mm/kasan/common.c:367
    kasan_slab_free include/linux/kasan.h:199 [inline]
    slab_free_hook mm/slub.c:1562 [inline]
    slab_free_freelist_hook+0x92/0x210 mm/slub.c:1600
    slab_free mm/slub.c:3161 [inline]
    kfree+0xe5/0x7f0 mm/slub.c:4213
    io_put_sq_data fs/io_uring.c:7095 [inline]
    io_sq_thread_finish+0x48e/0x5b0 fs/io_uring.c:7113
    io_ring_ctx_free fs/io_uring.c:8355 [inline]
    io_ring_exit_work+0x333/0xcf0 fs/io_uring.c:8525
    process_one_work+0x98d/0x1600 kernel/workqueue.c:2275
    worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
    kthread+0x3b1/0x4a0 kernel/kthread.c:292
    ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

    The buggy address belongs to the object at ffff88801d418c00
    which belongs to the cache kmalloc-512 of size 512
    The buggy address is located 120 bytes inside of
    512-byte region [ffff88801d418c00, ffff88801d418e00)
    The buggy address belongs to the page:
    page:00000000311e6f59 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1d418
    head:00000000311e6f59 order:2 compound_mapcount:0 compound_pincount:0
    flags: 0xfff00000010200(slab|head)
    raw: 00fff00000010200 dead000000000100 dead000000000122 ffff88800fc41c80
    raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
    page dumped because: kasan: bad access detected

    Memory state around the buggy address:
    ffff88801d418b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
    ffff88801d418b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
    >ffff88801d418c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
    ^
    ffff88801d418c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
    ffff88801d418d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
    ==================================================================


    Tested on:

    commit: dc5c40fb io_uring: always wait for sqd exited when stoppin..
    git tree: git://git.kernel.dk/linux-block io_uring-5.12
    console output: https://syzkaller.appspot.com/x/log.txt?x=111d175cd00000
    kernel config: https://syzkaller.appspot.com/x/.config?x=b3c6cab008c50864
    dashboard link: https://syzkaller.appspot.com/bug?extid=ac39856cb1b332dbbdda
    compiler:

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