Re: [PATCH 1/7] printk: Hand over printing to console if printing too long

From: Sergey Senozhatsky
Date: Thu Dec 10 2015 - 10:26:52 EST

On (12/10/15 23:52), Sergey Senozhatsky wrote:
> I think we better use raw_spin_lock as a print_lock; and, apart from that,
> seems that we don't re-init in zap_lock(). So I ended up with the following
> patch on top of yours (to be folded):
> - use raw_spin_lock
> - do not forget to re-init `print_lock' in zap_locks()

while we are on this, what do you guys think?

... spin_lock ... uart, etc panic

zap_lock() will raw_spin_lock_init(&logbuf_lock) and
sema_init(&console_sem, 1), but we still have `spin_lock'
held by con->write().

so the `panic' flush or print out will see con->write() being already


We do zap_lock() in printk to make a panic print out possible, but we
can end up having a locked serial console - e.g. panic has occurred
whilst CPUx was in con->write(), which takes some internal locks, thus
call_console_drivers() will perform con->write() on an already locked

Try to reset() every console in zap_lock() via console specific
->reset() call.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
include/linux/console.h | 1 +
kernel/printk/printk.c | 6 ++++++
2 files changed, 7 insertions(+)

diff --git a/include/linux/console.h b/include/linux/console.h
index bd19434..1cb8f72 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -125,6 +125,7 @@ struct console {
void (*unblank)(void);
int (*setup)(struct console *, char *);
int (*match)(struct console *, char *name, int idx, char *options);
+ void (*reset)(struct console *);
short flags;
short index;
int cflag;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f4a9565..ad172c4 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1580,6 +1580,7 @@ static void call_console_drivers(int level,
static void zap_locks(void)
+ struct console *c;
static unsigned long oops_timestamp;

if (time_after_eq(jiffies, oops_timestamp) &&
@@ -1589,6 +1590,11 @@ static void zap_locks(void)
oops_timestamp = jiffies;

+ for_each_console(c)
+ if ((c->flags & CON_ENABLED) && c->reset)
+ c->reset(c);
/* If a crash is occurring, make sure we can't deadlock */
/* And make sure that we print immediately */

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