From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: Question: cpuset_update_task_memory_state() and mmap_sem ??? From: Lee Schermerhorn In-Reply-To: <20070815230626.dac091b1.pj@sgi.com> References: <1187033902.5592.33.camel@localhost> <20070815230626.dac091b1.pj@sgi.com> Content-Type: text/plain Date: Thu, 16 Aug 2007 09:12:30 -0400 Message-Id: <1187269951.5900.3.camel@localhost> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Paul Jackson Cc: linux-mm@kvack.org List-ID: On Wed, 2007-08-15 at 23:06 -0700, Paul Jackson wrote: > Lee wrote: > > In the comment block for the subject function in cpuset.c, it notes that > > "This routine also might acquire callback_mutex and > > current->mm->mmap_sem." > > > > Is this is a stale comment? I can't find any path from this function to > > a down_{read|write}() on the caller's mmap_sem [in 23-rc2-mm2]. I > > suspect that one would have noticed, as > > cpuset_update_task_memory_state() is called from > > alloc_page_vma() which, according to its comment block, can only be > > called with the mmap_sem held [for read, at least]. > > Hmmm ... you may be right But I'm not sure. > > Obviously, the callback_mutex mention in the comment is correct, > but the current->mm->mmap_sem mention seems bogus. > > The routine mpol_rebind_task() is called from the last line of > cpuset_update_task_memory_state(). Whatever mmap_sem is taken > would be within that call. But I can't find any taking of > mmap_sem within or below mpol_rebind_task(), and all the code > paths in mm/mempolicy.c that do take mmap_sem locks seem to be > on unrelated code paths. > > I tried looking in a few old versions of kernel/cpuset.c and > mm/mempolicy.c to see if the mention of current->mm->mmap_sem > made more sense in some old version, but didn't see any version > of code that justified that comment. > > ... would you like to propose a patch, nuking the phrase: > > and current->mm->mmap_sem > > from that comment? If that's the correct thing to do, sure. Just wanted to check with you whether I was missing something. Lee > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org