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[ Upstream commit53d374979e] syzbot reported some bogus lockdep warnings, for example bad unlock balance in sch_direct_xmit(). They are due to a race condition between slow path and fast path, that is qdisc_xmit_lock_key gets re-registered in netdev_update_lockdep_key() on slow path, while we could still acquire the queue->_xmit_lock on fast path in this small window: CPU A CPU B __netif_tx_lock(); lockdep_unregister_key(qdisc_xmit_lock_key); __netif_tx_unlock(); lockdep_register_key(qdisc_xmit_lock_key); In fact, unlike the addr_list_lock which has to be reordered when the master/slave device relationship changes, queue->_xmit_lock is only acquired on fast path and only when NETIF_F_LLTX is not set, so there is likely no nested locking for it. Therefore, we can just get rid of re-registration of qdisc_xmit_lock_key. Reported-by: syzbot+4ec99438ed7450da6272@syzkaller.appspotmail.com Fixes:ab92d68fc2("net: core: add generic lockdep keys") Cc: Taehee Yoo <ap420073@gmail.com> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Acked-by: Taehee Yoo <ap420073@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.