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Tony Camuso 383035211c ipmi: move message error checking to avoid deadlock 
V1->V2: in handle_one_rcv_msg, if data_size > 2, set requeue to zero and
        goto out instead of calling ipmi_free_msg.
        Kosuke Tatsukawa <tatsu@ab.jp.nec.com>

In the source stack trace below, function set_need_watch tries to
take out the same si_lock that was taken earlier by ipmi_thread.

ipmi_thread() [drivers/char/ipmi/ipmi_si_intf.c:995]
 smi_event_handler() [drivers/char/ipmi/ipmi_si_intf.c:765]
  handle_transaction_done() [drivers/char/ipmi/ipmi_si_intf.c:555]
   deliver_recv_msg() [drivers/char/ipmi/ipmi_si_intf.c:283]
    ipmi_smi_msg_received() [drivers/char/ipmi/ipmi_msghandler.c:4503]
     intf_err_seq() [drivers/char/ipmi/ipmi_msghandler.c:1149]
      smi_remove_watch() [drivers/char/ipmi/ipmi_msghandler.c:999]
       set_need_watch() [drivers/char/ipmi/ipmi_si_intf.c:1066]

Upstream commit e1891cffd4 adds code to
ipmi_smi_msg_received() to call smi_remove_watch() via intf_err_seq()
and this seems to be causing the deadlock.

commit e1891cffd4
Author: Corey Minyard <cminyard@mvista.com>
Date:   Wed Oct 24 15:17:04 2018 -0500
    ipmi: Make the smi watcher be disabled immediately when not needed

The fix is to put all messages in the queue and move the message
checking code out of ipmi_smi_msg_received and into handle_one_recv_msg,
which processes the message checking after ipmi_thread releases its
locks.

Additionally,Kosuke Tatsukawa <tatsu@ab.jp.nec.com> reported that
handle_new_recv_msgs calls ipmi_free_msg when handle_one_rcv_msg returns
zero, so that the call to ipmi_free_msg in handle_one_rcv_msg introduced
another panic when "ipmitool sensor list" was run in a loop. He
submitted this part of the patch.

+free_msg:
+               requeue = 0;
+               goto out;

Reported by: Osamu Samukawa <osa-samukawa@tg.jp.nec.com>
Characterized by: Kosuke Tatsukawa <tatsu@ab.jp.nec.com>
Signed-off-by: Tony Camuso <tcamuso@redhat.com>
Fixes: e1891cffd4 ("ipmi: Make the smi watcher be disabled immediately when not needed")
Cc: stable@vger.kernel.org # 5.1
Signed-off-by: Corey Minyard <cminyard@mvista.com>
History 2019-08-22 11:08:13 -05:00
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README 

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.