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Date:   Fri, 6 Mar 2020 17:35:52 +0300
From:   Dan Carpenter <dan.carpenter@oracle.com>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        syzbot <syzbot+e017e49c39ab484ac87a@syzkaller.appspotmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>, io-uring@vger.kernel.org,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Thomas Gleixner <tglx@linutronix.de>, tony.luck@intel.com,
        the arch/x86 maintainers <x86@kernel.org>
Subject: Re: KASAN: use-after-free Read in percpu_ref_switch_to_atomic_rcu
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There a bunch of similar bugs.  It's seems a common anti-pattern.

block/blk-cgroup.c:85 blkg_free() warn: freeing 'blkg' which has percpu_ref_exit()
block/blk-core.c:558 blk_alloc_queue_node() warn: freeing 'q' which has percpu_ref_exit()
drivers/md/md.c:5528 md_free() warn: freeing 'mddev' which has percpu_ref_exit()
drivers/target/target_core_transport.c:583 transport_free_session() warn: freeing 'se_sess' which has percpu_ref_exit()
fs/aio.c:592 free_ioctx() warn: freeing 'ctx' which has percpu_ref_exit()
fs/aio.c:806 ioctx_alloc() warn: freeing 'ctx' which has percpu_ref_exit()
fs/io_uring.c:6115 io_sqe_files_unregister() warn: freeing 'data' which has percpu_ref_exit()
fs/io_uring.c:6431 io_sqe_files_register() warn: freeing 'ctx->file_data' which has percpu_ref_exit()
fs/io_uring.c:7134 io_ring_ctx_free() warn: freeing 'ctx' which has percpu_ref_exit()
kernel/cgroup/cgroup.c:4948 css_free_rwork_fn() warn: freeing 'css' which has percpu_ref_exit()
mm/backing-dev.c:615 cgwb_create() warn: freeing 'wb' which has percpu_ref_exit()

regards,
dan carpenter