Messages in this thread | | | Date | Wed, 6 Jan 2016 17:04:43 +0100 | From | Jiri Bohac <> | Subject | Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() |
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On Wed, Jan 06, 2016 at 08:00:33AM -0500, Prarit Bhargava wrote: > -ktime_t ktime_get_with_offset(enum tk_offsets offs) > +ktime_t ktime_get_with_offset(enum tk_offsets offs, int trylock) > { > struct timekeeper *tk = &tk_core.timekeeper; > unsigned int seq; > ktime_t base, *offset = offsets[offs]; > s64 nsecs; > + unsigned long flags = 0; > + > + if (unlikely(!timekeeping_initialized)) > + return ktime_set(0, 0); > > WARN_ON(timekeeping_suspended); > > + if (trylock && !raw_spin_trylock_irqsave(&timekeeper_lock, flags)) > + return ktime_set(KTIME_MAX, 0); > +
Are you trying to avoid a deadlock caused by calling printk() with timekeeper_lock locked?
I believe this is already unsafe, as explained in the commit log of 6d9bcb62 (timekeeping: use printk_deferred when holding timekeeping seqlock).
So directly calling ktime_get() from printk would just turn a rare deadlock into a certain one - perhaps a good thing?
-- Jiri Bohac <jbohac@suse.cz> SUSE Labs, SUSE CZ
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