Date: Sat, 09 Sep 2000 18:17:52 -0700 From: Peter Wemm <peter@netplex.com.au> To: Jason Evans <jasone@FreeBSD.org> Cc: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/kern kern_malloc.c Message-ID: <200009100117.e8A1HqG75602@netplex.com.au> In-Reply-To: <200009092227.PAA38766@freefall.freebsd.org>
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Jason Evans wrote:
> jasone 2000/09/09 15:27:35 PDT
>
> Modified files:
> sys/kern kern_malloc.c
> Log:
> Add a mutex to the malloc interfaces so that it can safely be called
> without owning the Giant lock.
Actually, this is even more deadly than I first thought..
s = splmem();
mtx_enter(&malloc_mtx, MTX_DEF);
while (ksp->ks_memuse >= ksp->ks_limit) {
....
tsleep((caddr_t)ksp, PSWP+2, type->ks_shortdesc, 0);
}
Behold, instant death. We must release all locks (except Giant) before
calling tsleep().
The calls to kmem_malloc() and kmem_free() etc must also be wrapped with
releasing the malloc mutex and obtaining Giant before the call, and backing
out again afterwards. The same for printf() etc.
I don't mean to pick on Jason, but this is a classic example of why we must
not rush into slapping locks all over the place without carefully mapping out
the interaction between locks, sleeps, locking protocol, etc.
Cheers,
-Peter
--
Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au
"All of this is for nothing if we don't go to the stars" - JMS/B5
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