On Fri, Jun 14, 2019 at 03:06:10PM +0200, Christian König wrote:
> Am 14.06.19 um 14:59 schrieb Peter Zijlstra:
> > +#define ww_mutex_lock_for_each(loop, pos, contended, ret, intr, ctx) \
> > + for (contended = ERR_PTR(-ENOENT); ({ \
> > + __label__ relock, next; \
> > + ret = -ENOENT; \
> > + if (contended == ERR_PTR(-ENOENT)) \
> > + contended = NULL; \
> > + else if (contended == ERR_PTR(-EDEADLK)) \
> > + contended = (pos); \
> > + else \
> > + goto next; \
> > + loop { \
> > + if (contended == (pos)) { \
> > + contended = NULL; \
> > + continue; \
> > + } \
> > +relock: \
> > + ret = !(intr) ? ww_mutex_lock(pos, ctx) : \
> > + ww_mutex_lock_interruptible(pos, ctx); \
> > + if (ret == -EDEADLK) { \
> > + ww_mutex_unlock_for_each(loop, pos, \
> > + contended); \
> > + contended = ERR_PTR(-EDEADLK); \
> > + goto relock; \
> >
> > while relock here continues where it left of and doesn't restart @loop.
> > Or am I reading this monstrosity the wrong way?
>
> contended = ERR_PTR(-EDEADLK) makes sure that the whole loop is restarted
> after retrying to acquire the lock.
>
> See the "if" above "loop".
ARGH, the loop inside the loop... Yeah, maybe, brain hurts.
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