Messages in this thread | | | Date | Thu, 24 Apr 2014 12:18:43 +0200 | From | Jan Kara <> | Subject | Re: [PATCH 2/8] printk: Release lockbuf_lock before calling console_trylock_for_printk() |
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On Wed 23-04-14 13:56:06, Andrew Morton wrote: > On Tue, 25 Mar 2014 18:54:55 +0100 Jan Kara <jack@suse.cz> wrote: > > > There's no reason to hold lockbuf_lock when entering > > console_trylock_for_printk(). The first thing this function does is > > calling down_trylock(console_sem) and if that fails it immediately > > unlocks lockbuf_lock. So lockbuf_lock isn't needed for that branch. > > When down_trylock() succeeds, the rest of console_trylock() is OK > > without lockbuf_lock (it is called without it from other places), and > > the only remaining thing in console_trylock_for_printk() is > > can_use_console() call. For that call console_sem is enough (it > > iterates all consoles and checks CON_ANYTIME flag). > > > > So we drop logbuf_lock before entering console_trylock_for_printk() > > which simplifies the code. > > > > I suppose we should document have_callable_console()'s locking > requirements, and I don't think that "early in boot" part is true? > > --- a/kernel/printk/printk.c~printk-release-lockbuf_lock-before-calling-console_trylock_for_printk-fix > +++ a/kernel/printk/printk.c > @@ -1377,7 +1377,9 @@ static void zap_locks(void) > sema_init(&console_sem, 1); > } > > -/* Check if we have any console registered that can be called early in boot. */ > +/* > + * Check if we have any console registered. Requires console_sem. So "early in boot" wasn't really exact but what you did isn't right either. What I'd put there is:
/* * Check if we have any console that is capable of printing while cpu is * booting or shutting down. Requires console_sem. */
Maybe the function name could be changed to reflect better what it does but I don't have any clever idea...
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
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