All of lore.kernel.org
 help / color / mirror / Atom feed
From: Pankaj Raghav <p.raghav@samsung.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@infradead.org>,
	Chaitanya Kulkarni <chaitanyak@nvidia.com>,
	linux-block@vger.kernel.org, Li Nan <linan666@huaweicloud.com>,
	dm-devel@redhat.com, Zdenek Kabelac <zkabelac@redhat.com>,
	p.raghav@samsung.com
Subject: Re: [dm-devel] [PATCH v2 1/3] brd: extend the rcu regions to cover read and write
Date: Thu, 27 Jul 2023 10:31:57 +0200	[thread overview]
Message-ID: <20230727083157.bwtndptv6rvoyezs@localhost> (raw)
In-Reply-To: <7d99fa-9c13-ab2a-acde-1f8bbc63bf3@redhat.com>

> Index: linux-2.6/drivers/block/brd.c
> ===================================================================
> --- linux-2.6.orig/drivers/block/brd.c
> +++ linux-2.6/drivers/block/brd.c
> @@ -150,23 +150,27 @@ static void copy_to_brd(struct brd_devic
>  	size_t copy;
>  
>  	copy = min_t(size_t, n, PAGE_SIZE - offset);
> +	rcu_read_lock();
>  	page = brd_lookup_page(brd, sector);

xa_load() inside brd_lookup_page() also calls rcu read lock. Instead of
nesting rcu locks, could we modify the brd_lookup_page to use:

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 970bd6ff38c4..acc37bfdd181 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -55,7 +55,9 @@ static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
        struct page *page;
 
        idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
-       page = xa_load(&brd->brd_pages, idx);
+
+       XA_STATE(xas, &brd->brd_pages, idx);
+       page = xas_load(&xas);
 
        BUG_ON(page && page->index != idx);

>  	BUG_ON(!page);
>  
>  	dst = kmap_atomic(page);
>  	memcpy(dst + offset, src, copy);
>  	kunmap_atomic(dst);

--
dm-devel mailing list
dm-devel@redhat.com
https://listman.redhat.com/mailman/listinfo/dm-devel


WARNING: multiple messages have this Message-ID (diff)
From: Pankaj Raghav <p.raghav@samsung.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>, Li Nan <linan666@huaweicloud.com>,
	Zdenek Kabelac <zkabelac@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	Chaitanya Kulkarni <chaitanyak@nvidia.com>,
	<linux-block@vger.kernel.org>, <dm-devel@redhat.com>,
	<p.raghav@samsung.com>
Subject: Re: [PATCH v2 1/3] brd: extend the rcu regions to cover read and write
Date: Thu, 27 Jul 2023 10:31:57 +0200	[thread overview]
Message-ID: <20230727083157.bwtndptv6rvoyezs@localhost> (raw)
In-Reply-To: <7d99fa-9c13-ab2a-acde-1f8bbc63bf3@redhat.com>

> Index: linux-2.6/drivers/block/brd.c
> ===================================================================
> --- linux-2.6.orig/drivers/block/brd.c
> +++ linux-2.6/drivers/block/brd.c
> @@ -150,23 +150,27 @@ static void copy_to_brd(struct brd_devic
>  	size_t copy;
>  
>  	copy = min_t(size_t, n, PAGE_SIZE - offset);
> +	rcu_read_lock();
>  	page = brd_lookup_page(brd, sector);

xa_load() inside brd_lookup_page() also calls rcu read lock. Instead of
nesting rcu locks, could we modify the brd_lookup_page to use:

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 970bd6ff38c4..acc37bfdd181 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -55,7 +55,9 @@ static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
        struct page *page;
 
        idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
-       page = xa_load(&brd->brd_pages, idx);
+
+       XA_STATE(xas, &brd->brd_pages, idx);
+       page = xas_load(&xas);
 
        BUG_ON(page && page->index != idx);

>  	BUG_ON(!page);
>  
>  	dst = kmap_atomic(page);
>  	memcpy(dst + offset, src, copy);
>  	kunmap_atomic(dst);

  reply	other threads:[~2023-07-27  8:41 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20230727083159eucas1p1c4b907caac8371200bbd465143ac39fd@eucas1p1.samsung.com>
2023-07-21 13:49 ` [dm-devel] [PATCH v2 1/3] brd: extend the rcu regions to cover read and write Mikulas Patocka
2023-07-21 13:49   ` Mikulas Patocka
2023-07-27  8:31   ` Pankaj Raghav [this message]
2023-07-27  8:31     ` Pankaj Raghav

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=20230727083157.bwtndptv6rvoyezs@localhost \
    --to=p.raghav@samsung.com \
    --cc=axboe@kernel.dk \
    --cc=chaitanyak@nvidia.com \
    --cc=dm-devel@redhat.com \
    --cc=hch@infradead.org \
    --cc=linan666@huaweicloud.com \
    --cc=linux-block@vger.kernel.org \
    --cc=mpatocka@redhat.com \
    --cc=zkabelac@redhat.com \
    /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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.