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Fri, 23 Oct 2020 06:12:26 -0400 X-MC-Unique: qaa83OiWNBWsXWKeB8gvyg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0F4801006CAF; Fri, 23 Oct 2020 10:12:25 +0000 (UTC) Received: from [10.36.114.18] (ovpn-114-18.ams2.redhat.com [10.36.114.18]) by smtp.corp.redhat.com (Postfix) with ESMTP id 249AD5B4BC; Fri, 23 Oct 2020 10:12:22 +0000 (UTC) Subject: Re: [PATCH] hugetlb: fix locking in region_add,region_cgh,allocate_file_region_entries To: Laurent Cremmer , Mike Kravetz Cc: Andrew Morton , Mina Almasry , David Rientjes , linux-mm@kvack.org, Shuah Khan References: <20201023074759.46605-1-laurent@oss.volkswagen.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Fri, 23 Oct 2020 12:12:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201023074759.46605-1-laurent@oss.volkswagen.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 23.10.20 09:47, Laurent Cremmer wrote: > commit 0db9d74ed884 ("hugetlb: disable region_add file_region coalescing") > introduced issues with regards to locking: > > - Missing spin_unlock in hugetlb.c:region_add and hugetlb.c:region_cgh > when returning after an error. > - Missing spin lock in hugetlb.c:allocate_file_region_entries > when returning after an error. > > The first two errors were spotted using the coccinelle static code > analysis tool while focusing on the mini_lock.cocci script, > whose goal is to find missing unlocks. > > make coccicheck mode=REPORT m=mm/hugetlb.c > > mm/hugetlb.c:514:3-9: preceding lock on line 487 > mm/hugetlb.c:564:2-8: preceding lock on line 554 > > The third instance spotted by manual examination. > > 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. > > This patch reintroduces the original error path making sure the lock is > properly released on all exits. > > 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. > > This patch ensures that the lock will be reacquired in the error path also. > > Fixes: 0db9d74ed884 ("hugetlb: disable region_add file_region coalescing") > Link: https://lists.elisa.tech/g/development-process/message/289 > Signed-off-by: Laurent Cremmer > Reviewed-by: Oliver Hartkopp > --- > mm/hugetlb.c | 17 +++++++++++------ > 1 file changed, 11 insertions(+), 6 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index fe76f8fd5a73..92bea6f77361 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -438,7 +438,7 @@ static int allocate_file_region_entries(struct resv_map *resv, > for (i = 0; i < to_allocate; i++) { > trg = kmalloc(sizeof(*trg), GFP_KERNEL); So we're allocating memory with GFP_KERNEL while holding a spinlock? If my memory isn't completely wrong, that's broken, no? this would require GFP_ATOMIC? But I might be messing up things :) > if (!trg) > - goto out_of_memory; > + goto out_of_memory_unlocked; > list_add(&trg->link, &allocated_regions); > } > > @@ -450,7 +450,8 @@ static int allocate_file_region_entries(struct resv_map *resv, > > return 0; > > -out_of_memory: > +out_of_memory_unlocked: > + spin_lock(&resv->lock); > list_for_each_entry_safe(rg, trg, &allocated_regions, link) { > list_del(&rg->link); > kfree(rg); > @@ -508,7 +509,8 @@ static long region_add(struct resv_map *resv, long f, long t, > > if (allocate_file_region_entries( > resv, actual_regions_needed - in_regions_needed)) { > - return -ENOMEM; > + add = -ENOMEM; dito, does this handle atomic context? > + goto out_locked; > } > > goto retry; > @@ -517,7 +519,7 @@ static long region_add(struct resv_map *resv, long f, long t, > add = add_reservation_in_range(resv, f, t, h_cg, h, NULL); > > resv->adds_in_progress -= in_regions_needed; > - > +out_locked: > spin_unlock(&resv->lock); > VM_BUG_ON(add < 0); > return add; > @@ -557,11 +559,14 @@ static long region_chg(struct resv_map *resv, long f, long t, > if (*out_regions_needed == 0) > *out_regions_needed = 1; > > - if (allocate_file_region_entries(resv, *out_regions_needed)) > - return -ENOMEM; > + if (allocate_file_region_entries(resv, *out_regions_needed)) { > + chg = -ENOMEM; > + goto out_locked; > + } dito -- Thanks, David / dhildenb