LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Herbert Xu <herbert@gondor.apana.org.au>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alan Stern <stern@rowland.harvard.edu>,
	"Paul E. McKenney" <paulmck@linux.ibm.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Fengguang Wu <fengguang.wu@intel.com>, LKP <lkp@01.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Netdev <netdev@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Andrea Parri <andrea.parri@amarulasolutions.com>,
	Luc Maranget <luc.maranget@inria.fr>,
	Jade Alglave <j.alglave@ucl.ac.uk>
Subject: inet: frags: Turn fqdir->dead into an int for old Alphas
Date: Fri, 7 Jun 2019 22:09:49 +0800
Message-ID: <20190607140949.tzwyprrhmqdx33iu@gondor.apana.org.au> (raw)
In-Reply-To: <CAHk-=wgGnCw==uY8radrB+Tg_CEmzOtwzyjfMkuh7JmqFh+jzQ@mail.gmail.com>

On Tue, Jun 04, 2019 at 09:04:55AM -0700, Linus Torvalds wrote:
>
> In fact, the alpha port was always subtly buggy exactly because of the
> "byte write turns into a read-and-masked-write", even if I don't think
> anybody ever noticed (we did fix cases where people _did_ notice,
> though, and we might still have some cases where we use 'int' for
> booleans because of alpha issues.).

This is in fact a real bug in the code in question that no amount
of READ_ONCE/WRITE_ONCE would have caught.  The field fqdir->dead is
declared as boolean so writing to it is not atomic (on old Alphas).

I don't think it currently matters because padding would ensure
that it is in fact 64 bits long.  However, should someone add another
char/bool/bitfield in this struct in future it could become an issue.

So let's fix it.

---8<--
The field fqdir->dead is meant to be written (and read) atomically.
As old Alpha CPUs can't write a single byte atomically, we need at
least an int for it to work.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index e91b79ad4e4a..8c458fba74ad 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -14,7 +14,9 @@ struct fqdir {
 	int			max_dist;
 	struct inet_frags	*f;
 	struct net		*net;
-	bool			dead;
+
+	/* We can't use boolean because this needs atomic writes. */
+	int			dead;
 
 	struct rhashtable       rhashtable ____cacheline_aligned_in_smp;
 
diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 35e9784fab4e..05aa7c145817 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -193,7 +193,7 @@ void fqdir_exit(struct fqdir *fqdir)
 {
 	fqdir->high_thresh = 0; /* prevent creation of new frags */
 
-	fqdir->dead = true;
+	fqdir->dead = 1;
 
 	/* call_rcu is supposed to provide memory barrier semantics,
 	 * separating the setting of fqdir->dead with the destruction
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

  parent reply index

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-10  0:57 [rcu] kernel BUG at include/linux/pagemap.h:149! Fengguang Wu
2015-09-10 10:25 ` Boqun Feng
2015-09-10 17:16   ` Paul E. McKenney
2015-09-11  2:19     ` Boqun Feng
     [not found]       ` <CAJzB8QG=1iZW3dQEie6ZSTLv8GZ3YSut0aL1VU7LLmiHQ1B1DQ@mail.gmail.com>
2015-09-11 21:59         ` Paul E. McKenney
2015-09-12  5:46           ` Boqun Feng
2015-09-21 19:30       ` Frederic Weisbecker
2015-09-21 20:43         ` Paul E. McKenney
2019-06-02  5:56           ` rcu_read_lock lost its compiler barrier Herbert Xu
2019-06-02 20:54             ` Linus Torvalds
2019-06-03  2:46               ` Herbert Xu
2019-06-03  3:47                 ` Paul E. McKenney
2019-06-03  4:01                   ` Herbert Xu
2019-06-03  4:17                     ` Herbert Xu
2019-06-03  7:23                     ` Paul E. McKenney
2019-06-03  8:42                       ` Paul E. McKenney
2019-06-03 15:26                         ` David Laight
2019-06-03 15:40                           ` Linus Torvalds
2019-06-03  5:26                   ` Herbert Xu
2019-06-03  6:42                     ` Boqun Feng
2019-06-03 20:03                       ` Paul E. McKenney
2019-06-04 14:44                         ` Alan Stern
2019-06-04 16:04                           ` Linus Torvalds
2019-06-04 17:00                             ` Alan Stern
2019-06-04 17:29                               ` Linus Torvalds
2019-06-07 14:09                             ` Herbert Xu [this message]
2019-06-07 15:26                               ` inet: frags: Turn fqdir->dead into an int for old Alphas Eric Dumazet
2019-06-07 15:32                                 ` Herbert Xu
2019-06-07 16:13                                   ` Eric Dumazet
2019-06-07 16:19                                 ` Linus Torvalds
2019-06-08 15:27                                   ` Paul E. McKenney
2019-06-08 17:42                                     ` Linus Torvalds
2019-06-08 17:50                                       ` Linus Torvalds
2019-06-08 18:50                                         ` Paul E. McKenney
2019-06-08 18:14                                       ` Paul E. McKenney
2019-06-06  4:51                           ` rcu_read_lock lost its compiler barrier Herbert Xu
2019-06-06  6:05                             ` Paul E. McKenney
2019-06-06  6:14                               ` Herbert Xu
2019-06-06  9:06                                 ` Paul E. McKenney
2019-06-06  9:28                                   ` Herbert Xu
2019-06-06 10:58                                     ` Paul E. McKenney
2019-06-06 13:38                                       ` Herbert Xu
2019-06-06 13:48                                         ` Paul E. McKenney
2019-06-06  8:16                           ` Andrea Parri
2019-06-06 14:19                             ` Alan Stern
2019-06-08 15:19                               ` Paul E. McKenney
2019-06-08 15:56                                 ` Alan Stern
2019-06-08 16:31                                   ` Paul E. McKenney
2019-06-03  9:35                     ` Paul E. McKenney
2019-06-06  8:38                 ` Andrea Parri
2019-06-06  9:32                   ` Herbert Xu
2019-06-03  0:06             ` Paul E. McKenney
2019-06-03  3:03               ` Herbert Xu
2019-06-03  9:27                 ` Paul E. McKenney
2019-06-03 15:55                 ` Linus Torvalds
2019-06-03 16:07                   ` Linus Torvalds
2019-06-03 19:53                     ` Paul E. McKenney
2019-06-03 20:24                       ` Linus Torvalds
2019-06-04 21:14                         ` Paul E. McKenney
2019-06-05  2:21                           ` Herbert Xu
2019-06-05  3:30                             ` Paul E. McKenney
2019-06-06  4:37                               ` Herbert Xu

Reply instructions:

You may reply publically 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=20190607140949.tzwyprrhmqdx33iu@gondor.apana.org.au \
    --to=herbert@gondor.apana.org.au \
    --cc=andrea.parri@amarulasolutions.com \
    --cc=boqun.feng@gmail.com \
    --cc=davem@davemloft.net \
    --cc=fengguang.wu@intel.com \
    --cc=fweisbec@gmail.com \
    --cc=j.alglave@ucl.ac.uk \
    --cc=linux-kernel@vger.kernel.org \
    --cc=lkp@01.org \
    --cc=luc.maranget@inria.fr \
    --cc=netdev@vger.kernel.org \
    --cc=paulmck@linux.ibm.com \
    --cc=stern@rowland.harvard.edu \
    --cc=torvalds@linux-foundation.org \
    /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

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git