From: Tejun Heo <tj@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: security@kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, linux-mm@kvack.org,
torvalds@linux-foundation.org, jannh@google.com,
paulmck@linux.vnet.ibm.com, bcrl@kvack.org,
viro@zeniv.linux.org.uk, kent.overstreet@gmail.com
Subject: Re: [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup
Date: Mon, 26 Mar 2018 07:54:31 -0700 [thread overview]
Message-ID: <20180326145431.GC1840639@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <20180314194515.1661824-4-tj@kernel.org>
Hello, Andrew.
Do you mind picking up the following patch? I can't find a good tree
to route this through. The raw patch can be found at
https://marc.info/?l=linux-mm&m=152105674112496&q=raw
Thank you very much.
On Wed, Mar 14, 2018 at 12:45:11PM -0700, Tejun Heo wrote:
> hmm_devmem_find() requires rcu_read_lock_held() but there's nothing
> which actually uses the RCU protection. The only caller is
> hmm_devmem_pages_create() which already grabs the mutex and does
> superflous rcu_read_lock/unlock() around the function.
>
> This doesn't add anything and just adds to confusion. Remove the RCU
> protection and open-code the radix tree lookup. If this needs to
> become more sophisticated in the future, let's add them back when
> necessary.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: linux-mm@kvack.org
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> ---
> Hello,
>
> Jérôme, how do you want to route this patch? If you prefer, I can
> route it together with other patches.
>
> Thanks.
>
> mm/hmm.c | 12 ++----------
> 1 file changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 320545b98..d4627c5 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -845,13 +845,6 @@ static void hmm_devmem_release(struct device *dev, void *data)
> hmm_devmem_radix_release(resource);
> }
>
> -static struct hmm_devmem *hmm_devmem_find(resource_size_t phys)
> -{
> - WARN_ON_ONCE(!rcu_read_lock_held());
> -
> - return radix_tree_lookup(&hmm_devmem_radix, phys >> PA_SECTION_SHIFT);
> -}
> -
> static int hmm_devmem_pages_create(struct hmm_devmem *devmem)
> {
> resource_size_t key, align_start, align_size, align_end;
> @@ -892,9 +885,8 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem)
> for (key = align_start; key <= align_end; key += PA_SECTION_SIZE) {
> struct hmm_devmem *dup;
>
> - rcu_read_lock();
> - dup = hmm_devmem_find(key);
> - rcu_read_unlock();
> + dup = radix_tree_lookup(&hmm_devmem_radix,
> + key >> PA_SECTION_SHIFT);
> if (dup) {
> dev_err(device, "%s: collides with mapping for %s\n",
> __func__, dev_name(dup->device));
> --
> 2.9.5
>
--
tejun
next prev parent reply other threads:[~2018-03-26 14:54 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-14 19:41 [PATCHSET v2] percpu_ref, RCU: Audit RCU usages in percpu_ref users Tejun Heo
2018-03-14 19:45 ` [PATCH 1/8] fs/aio: Add explicit RCU grace period when freeing kioctx Tejun Heo
2018-03-14 19:45 ` [PATCH 2/8] fs/aio: Use RCU accessors for kioctx_table->table[] Tejun Heo
2018-03-14 19:45 ` [PATCH 3/8] RDMAVT: Fix synchronization around percpu_ref Tejun Heo
2018-03-15 22:24 ` Jason Gunthorpe
2018-03-14 19:45 ` [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup Tejun Heo
2018-03-26 14:54 ` Tejun Heo [this message]
2018-03-27 16:12 ` Jerome Glisse
2018-03-14 19:45 ` [PATCH 5/8] percpu_ref: Update doc to dissuade users from depending on internal RCU grace periods Tejun Heo
2018-03-19 17:10 ` Tejun Heo
2018-03-14 19:45 ` [PATCH 6/8] RCU, workqueue: Implement rcu_work Tejun Heo
2018-03-14 20:13 ` Paul E. McKenney
2018-03-16 6:01 ` Lai Jiangshan
2018-03-19 16:45 ` Tejun Heo
2018-03-20 10:04 ` Lai Jiangshan
2018-03-14 19:45 ` [PATCH 7/8] cgroup: Use rcu_work instead of explicit rcu and work item Tejun Heo
2018-03-14 19:45 ` [PATCH 8/8] fs/aio: " Tejun Heo
2018-03-19 17:12 ` Tejun Heo
2018-03-21 15:58 ` Oleg Nesterov
2018-03-21 16:40 ` Tejun Heo
2018-03-21 17:17 ` Oleg Nesterov
2018-03-21 17:53 ` Tejun Heo
2018-03-22 11:24 ` Oleg Nesterov
2018-03-26 15:04 ` Tejun Heo
2018-03-27 14:28 ` Oleg Nesterov
2018-03-27 15:55 ` Tejun Heo
2018-03-29 16:49 ` Oleg Nesterov
2018-03-29 17:41 ` Tejun Heo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180326145431.GC1840639@devbig577.frc2.facebook.com \
--to=tj@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=bcrl@kvack.org \
--cc=jannh@google.com \
--cc=kent.overstreet@gmail.com \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=paulmck@linux.vnet.ibm.com \
--cc=security@kernel.org \
--cc=torvalds@linux-foundation.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).