Messages in this thread Patch in this message | | | Date | Fri, 11 Dec 2015 00:24:34 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH 1/7] printk: Hand over printing to console if printing too long |
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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?
CPU1 CPU2 console_unlock() call_console_drivers() con->write() ... 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 blocked.
===8<====
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 console.
Try to reset() every console in zap_lock() via console specific ->reset() call.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> --- 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; debug_locks_off(); + + 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 */ raw_spin_lock_init(&logbuf_lock); /* And make sure that we print immediately */ -- 2.6.3
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