From: David Laight <David.Laight@ACULAB.COM>
To: 'Herbert Xu' <herbert@gondor.apana.org.au>,
Jakub Kicinski <jakub.kicinski@netronome.com>,
"davem@davemloft.net" <davem@davemloft.net>,
"tgraf@suug.ch" <tgraf@suug.ch>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"oss-drivers@netronome.com" <oss-drivers@netronome.com>,
"neilb@suse.com" <neilb@suse.com>,
Simon Horman <simon.horman@netronome.com>
Subject: RE: [PATCH 2/2] rhashtable: Fix cmpxchg RCU warnings
Date: Thu, 16 May 2019 09:20:36 +0000 [thread overview]
Message-ID: <e79357ea8fde45b281be9a8196b806f8@AcuMS.aculab.com> (raw)
In-Reply-To: <E1hRAg8-0004Fy-0O@gondobar>
From: Herbert Xu
> Sent: 16 May 2019 08:20
> As cmpxchg is a non-RCU mechanism it will cause sparse warnings
> when we use it for RCU. This patch adds explicit casts to silence
> those warnings. This should probably be moved to RCU itself in
> future.
>
...
> - if (cmpxchg(prev, NULL, ntbl) == NULL)
> + if (cmpxchg((union nested_table **)prev, NULL, ntbl) == NULL)
I presume these casts remove an 'rcu' marker on the variable.
Is there a way of marking such casts as 'for sparse only' so
that the compiler does proper type checking.
(Clearly this isn't that relevant here as the cast could be (void **).)
Hmmm something should be checking that the type of the argument
to cmpxchg is 'pointer to "something the size of a pointer"'
Adding any kind of cast subverts that test.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2019-05-16 9:20 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-15 20:55 [PATCH net] rhashtable: fix sparse RCU warnings on bit lock in bucket pointer Jakub Kicinski
2019-05-15 21:42 ` NeilBrown
2019-05-15 22:04 ` Jakub Kicinski
2019-05-16 5:16 ` Herbert Xu
2019-05-16 7:18 ` [PATCH 0/2] rhashtable: Fix sparse warnings Herbert Xu
2019-05-16 16:45 ` David Miller
2019-05-16 7:19 ` [PATCH 1/2] rhashtable: Remove RCU marking from rhash_lock_head Herbert Xu
2019-05-16 7:19 ` [PATCH 2/2] rhashtable: Fix cmpxchg RCU warnings Herbert Xu
2019-05-16 9:20 ` David Laight [this message]
2019-05-16 12:42 ` Herbert Xu
2019-05-16 15:19 ` [PATCH net] rhashtable: fix sparse RCU warnings on bit lock in bucket pointer Jakub Kicinski
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