Date: Wed, 13 Dec 2000 10:52:48 -0800 (PST) From: Matt Dillon <dillon@earth.backplane.com> To: bright@wintelcom.net Cc: tanimura@FreeBSD.ORG, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG, jhb@FreeBSD.ORG, cp@FreeBSD.ORG Subject: Re: cvs commit: src/sys/ufs/ffs ffs_vfsops.c Message-ID: <200012131852.eBDIqm584821@earth.backplane.com> References: <200012131003.eBDA3rh34394@freefall.freebsd.org> <20001213024954.B16205@fw.wintelcom.net> <vm4s088s2l.wl@rina.r.dl.itc.u-tokyo.ac.jp>
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:Thus it should be even better to enter to and exit from the ufs hash
:mutex in the functions shown above.
:
:Alfred> That maybe the code should be using wakeup_one() as well? I'm
:Alfred> not sure how wakeup_one works with respect to FIFO or LIFO,
:Alfred> if it's LIFO then this can cause problems because of lots of
:Alfred> processes wedged on this getting stuck behind the newcomers.
:Alfred> If it's FIFO we should be fine.
:
:A sleep queue is a TAILQ, which is FIFO. So wakeup_one() should work.
:
:--
:Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> <tanimura@FreeBSD.org>
I have one request here. In order for wakeup_one() to work, any
waiting tasks *must* attempt to obtain the lock when they are woken up
rather then (potentially) abort and do something else, or no other
task will be woken up.
I would like all instances where tasks wait here, or in the single
instance if we are talking about a centralized locking routine, to
document this requirement in a comment.
We do not want to run up against the situation where some future
programmer believes he can wait for a lock and then abort when he
is woken up (e.g. if getting a signal) rather then actually obtain
the lock.
-Matt
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