3.16.51-rc1 review patch. If anyone has any objections, please let me know.
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From: Matt Redfearn matt.redfearn@imgtec.com
commit 2b1be689f3aadcfe0a768314c80e43483c784659 upstream.
Commit 4c30c6f566c0 ("kernel/printk: do not turn off bootconsole in printk_late_init() if keep_bootcon") added a check on keep_bootcon to ensure that boot consoles were kept around until the real console is registered.
This can lead to problems if the boot console data and code are in the init section, since it can be freed before the boot console is unregistered.
Commit 81cc26f2bd11 ("printk: only unregister boot consoles when necessary") fixed this a better way. It allowed to keep boot consoles that did not use init data. Unfortunately it did not remove the check of keep_bootcon.
This can lead to crashes and weird panics when the bootconsole is accessed after free, especially if page poisoning is in use and the code / data have been overwritten with a poison value.
To prevent this, always free the boot console if it is within the init section. In addition, print a warning about that the console is removed prematurely.
Finally there is a new comment how to avoid the warning. It replaced an explanation that duplicated a more comprehensive function description few lines above.
Fixes: 4c30c6f566c0 ("kernel/printk: do not turn off bootconsole in printk_late_init() if keep_bootcon") Link: http://lkml.kernel.org/r/1500036673-7122-2-git-send-email-pmladek@suse.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Jiri Slaby jslaby@suse.com Cc: "David S. Miller" davem@davemloft.net Cc: Alan Cox gnomes@lxorguk.ukuu.org.uk Cc: "Fabio M. Di Nitto" fdinitto@redhat.com Cc: linux-serial@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Matt Redfearn matt.redfearn@imgtec.com [pmladek@suse.com: print the warning, code and comments clean up] Reviewed-by: Sergey Senozhatsky sergey.senozhatsky@gmail.com Signed-off-by: Petr Mladek pmladek@suse.com Signed-off-by: Ben Hutchings ben@decadent.org.uk --- kernel/printk/printk.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-)
--- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2570,25 +2570,23 @@ EXPORT_SYMBOL(unregister_console); * makes it difficult to diagnose problems that occur during this time. * * To mitigate this problem somewhat, only unregister consoles whose memory - * intersects with the init section. Note that code exists elsewhere to get - * rid of the boot console as soon as the proper console shows up, so there - * won't be side-effects from postponing the removal. + * intersects with the init section. Note that all other boot consoles will + * get unregistred when the real preferred console is registered. */ static int __init printk_late_init(void) { struct console *con;
for_each_console(con) { - if (!keep_bootcon && con->flags & CON_BOOT) { + if ((con->flags & CON_BOOT) && + init_section_intersects(con, sizeof(*con))) { /* - * Make sure to unregister boot consoles whose data - * resides in the init section before the init section - * is discarded. Boot consoles whose data will stick - * around will automatically be unregistered when the - * proper console replaces them. + * Please, consider moving the reported consoles out + * of the init section. */ - if (init_section_intersects(con, sizeof(*con))) - unregister_console(con); + pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n", + con->name, con->index); + unregister_console(con); } } hotcpu_notifier(console_cpu_notify, 0);