malloc.9 locking section

[John Baldwin]

On 08-Apr-2003 Alan Cox wrote:
> On Tue, Apr 08, 2003 at 03:31:40PM -0400, John Baldwin wrote:
>> 
>> On 17-Mar-2003 Harti Brandt wrote:
>> > Index: malloc.9
>> > ===================================================================
>> > RCS file: /home/ncvs/src/share/man/man9/malloc.9,v
>> > retrieving revision 1.30
>> > diff -u -r1.30 malloc.9
>> > --- malloc.9  24 Feb 2003 05:53:27 -0000      1.30
>> > +++ malloc.9  17 Mar 2003 15:06:14 -0000
>> >
>> > [snip]
>> 
>> Looks good to me.  While you are at it, please kill the following
>> from the manpage (if you aren't already doing so):
>> 
>>      Any calls to malloc() or free() when holding a vnode(9) interlock, will
>>      cause a LOR (Lock Order Reversal) due to the interwining of VM Objects
>>      and Vnodes.
>> 
> 
> Why?  The above statement is true.

It's highly specific.  Harti is adding wording to say "don't hold any
locks when calling malloc() with M_WAITOK," not just vnode interlocks.
If vnode interlocks are even a problem with M_NOWAIT, then perhaps you
could add wording for that case to Harti's statement ("even with M_NOWAIT
one cannot hold vnode interlocks...").  My main concern is that I don't want
a situation where malloc(9) grows a huge laundry list of all the locks
in the kernel saying that can't be held when it is called.  Such a list
would be hard to maintain and would easily rot, be incomplete, etc.

-- 

John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/