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From: Laurent Cremmer <laurent@oss.volkswagen.com>
To: Oscar Salvador <osalvador@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	 Mina Almasry <almasrymina@google.com>,
	David Rientjes <rientjes@google.com>,
	linux-mm@kvack.org,  Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH] hugetlb: fix locking in region_add,region_cgh,allocate_file_region_entries
Date: Fri, 23 Oct 2020 13:32:54 +0200	[thread overview]
Message-ID: <CAPHd0UAxtkV4sPobwvdvrmoGaaru3ib81-=o9-V0dV4h2sorvA@mail.gmail.com> (raw)
In-Reply-To: <20201023110204.GA3925@linux>

>
> On Fri, Oct 23, 2020 at 09:47:59AM +0200, Laurent Cremmer wrote:
> > The third instance spotted by manual examination.
>
> It is friday, I might be overlooking something obvious, so bear with me.
>
> > In static long region_add(...) and static long region_cgh(...) , releasing
> > the acquired lock when exiting via their error path was removed.
> > This will cause these functions to return with a lock held if they do not
> > succeed.
>
> If they do not suceed, it means that allocate_file_region_entries returned
> non-zero, which means that we hit:
>
>         spin_unlock(&resv->lock);
>         for (i = 0; i < to_allocate; i++) {
>                 trg = kmalloc(sizeof(*trg), GFP_KERNEL);
>                 if (!trg)
>                         goto out_of_memory;
>                 list_add(&trg->link, &allocated_regions);
>          }
>
> So, we do spin_unlock before jumping to out_of_memory.
>
> > A a new function allocate_file_region_entries was also introduced  that
> > must be called with a lock held and returned with the lock held.
> > However the lock is temporarily released during processing but will not
> > be reacquired on error.
>
> As stated above, region_add/region_chr exit immediately on allocate_file_region_entries
> failure, so it does not need to acquire the lock.
>

I came to the same conclusion with the help of David's remarks :-) .
And in the end, this patch would be more about fixing the readability
of the code than fixing a live problem per-se. If it ain't broken,
don't fix it as they say :-)

It is friday, so thanks for taking the time to look into this.

>
> --
> Oscar Salvador
> SUSE L3


  reply	other threads:[~2020-10-23 11:33 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-23  7:47 [PATCH] hugetlb: fix locking in region_add,region_cgh,allocate_file_region_entries Laurent Cremmer
2020-10-23 10:12 ` David Hildenbrand
2020-10-23 11:25   ` Laurent Cremmer
2020-10-23 11:39     ` David Hildenbrand
2020-10-23 11:02 ` Oscar Salvador
2020-10-23 11:32   ` Laurent Cremmer [this message]
2020-10-23 12:11     ` Oscar Salvador
2020-10-23 16:47       ` Mike Kravetz
2020-10-27  7:34         ` Laurent Cremmer
2020-10-28 19:18 ` Mina Almasry

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