@@ -23,6 +23,7 @@
#include <linux/sysrq.h>
#include <linux/init.h>
#include <linux/nmi.h>
+#include <linux/console.h>
#define PANIC_TIMER_STEP 100
#define PANIC_BLINK_SPD 18
@@ -145,6 +146,15 @@ void panic(const char *fmt, ...)
bust_spinlocks(0);
+ /*
+ * We may have ended up stopping the CPU holding the lock (in
+ * smp_send_stop()) while still having some valuable data in the console
+ * buffer. Try to acquire the lock then release it regardless of the
+ * result. The release will also print the buffers out.
+ */
+ console_trylock();
+ console_unlock();
+
if (!panic_blink)
panic_blink = no_blink;
This is a note to let you know that I have just added a patch titled panic: release stale console lock to always get the logbuf printed out to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt24. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ---8<------------------------------------------------------------ From c7afd462eae6d9541369e6a2370aec6dc62672ca Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov <vkuznets@redhat.com> Date: Fri, 6 Nov 2015 16:32:58 -0800 Subject: panic: release stale console lock to always get the logbuf printed out commit 08d78658f393fefaa2e6507ea052c6f8ef4002a2 upstream. In some cases we may end up killing the CPU holding the console lock while still having valuable data in logbuf. E.g. I'm observing the following: - A crash is happening on one CPU and console_unlock() is being called on some other. - console_unlock() tries to print out the buffer before releasing the lock and on slow console it takes time. - in the meanwhile crashing CPU does lots of printk()-s with valuable data (which go to the logbuf) and sends IPIs to all other CPUs. - console_unlock() finishes printing previous chunk and enables interrupts before trying to print out the rest, the CPU catches the IPI and never releases console lock. This is not the only possible case: in VT/fb subsystems we have many other console_lock()/console_unlock() users. Non-masked interrupts (or receiving NMI in case of extreme slowness) will have the same result. Getting the whole console buffer printed out on crash should be top priority. [akpm@linux-foundation.org: tweak comment text] Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Baoquan He <bhe@redhat.com> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Xie XiuQi <xiexiuqi@huawei.com> Cc: Seth Jennings <sjenning@redhat.com> Cc: "K. Y. Srinivasan" <kys@microsoft.com> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- kernel/panic.c | 10 ++++++++++ 1 file changed, 10 insertions(+)