Date: Tue, 24 Feb 2004 08:11:25 -0800 (PST) From: Don Lewis <truckman@FreeBSD.org> To: jhb@FreeBSD.org Cc: cg@FreeBSD.org Subject: Re: exclusive sleep mutex pcm0 (sound cdev) r = 0 Message-ID: <200402241611.i1OGBP7E074494@gw.catspoiler.org> In-Reply-To: <200402241058.39196.jhb@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 24 Feb, John Baldwin wrote:
> On Tuesday 24 February 2004 10:52 am, Don Lewis wrote:
>> On 24 Feb, John Baldwin wrote:
>> > Eek, why not a sx lock if you must go to a sleepable lock?
>>
>> That was my initial thought, but I was scared off by the following
>> statement in the sx(9) man page:
>>
>> A thread may not own a shared lock and an exclusive lock
>> simultaneously; attempting to do so will result in deadlock.
>>
>> My plan is to hold this lock across large portions of the open() and
>> ioctl() methods (and possibly read() and write() as well). Some of
>> these may call code outside of my direct control, such as methods in the
>> hardware specific drivers, as well as things like malloc(). I'm
>> concerned about causing a deadlock by violating the sx usage rules.
>
> It means on the same lock, i.e. you can't try to do sx_slock(&foo) and then do
> sx_xlock(&foo). You can mix shared/exclusive of different locks ok.
Cool! I'll make it an sx lock.
The man page should probably be clarified, maybe something like:
A thread must not attempt to acquire a lock both shared and
exclusive at the same time. Such an attempt will result in a
deadlock.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200402241611.i1OGBP7E074494>