linux-kernel - [RFC][PATCH 0/2] Access console drivers list under console

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Message-Id: <20190423062511.1118-1-sergey.senozhatsky@gmail.com>
Date:   Tue, 23 Apr 2019 15:25:09 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: [RFC][PATCH 0/2] Access console drivers list under console_sem

Petr, Steven,

	RFC

	Normally, we grab console_sem lock before we iterate consoles
list, which is necessary if we want to be race free. The only exception
to this rule is console_flush_on_panic(). However, it seems that we are
not fully race free - register_console() iterates console drivers list
in unsafe manner in several places. E.g. the following scenarion:

	CPU0					CPU1
	register_console()			unregister_console()
						 console_lock()
	  for_each_console()			  // modify console_drivers
	    con->foo				    kfree(con)

So I have two quick-n-dirty patches, which remove unsafe console list
access.

What do you think?

Sergey Senozhatsky (2):
  printk: lock console_sem before we unregister boot consoles
  printk: take console_sem when accessing console drivers list

 kernel/printk/printk.c | 117 ++++++++++++++++++++++++-----------------
 1 file changed, 69 insertions(+), 48 deletions(-)

-- 
2.21.0