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[51.6.142.41]) by smtp.gmail.com with ESMTPSA id r6sm25367610wrq.92.2020.01.15.05.56.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jan 2020 05:56:33 -0800 (PST) Date: Wed, 15 Jan 2020 13:56:31 +0000 From: Wei Liu To: madhuparnabhowmik04@gmail.com Cc: wei.liu@kernel.org, paul@xen.org, davem@davemloft.net, xen-devel@lists.xenproject.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, paulmck@kernel.org, joel@joelfernandes.org, frextrite@gmail.com, linux-kernel-mentees@lists.linuxfoundation.org Subject: Re: [PATCH] net: xen-netbank: hash.c: Use built-in RCU list checking Message-ID: <20200115135631.edr2nrfkycppxcku@debian> References: <20200115124129.5684-1-madhuparnabhowmik04@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200115124129.5684-1-madhuparnabhowmik04@gmail.com> User-Agent: NeoMutt/20180716 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Thanks for the patch. There is a typo in the subject line. It should say xen-netback, not xen-netbank. On Wed, Jan 15, 2020 at 06:11:28PM +0530, madhuparnabhowmik04@gmail.com wrote: > From: Madhuparna Bhowmik > > list_for_each_entry_rcu has built-in RCU and lock checking. > Pass cond argument to list_for_each_entry_rcu. > > Signed-off-by: Madhuparna Bhowmik > --- > drivers/net/xen-netback/hash.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/xen-netback/hash.c b/drivers/net/xen-netback/hash.c > index 10d580c3dea3..30709bc9d170 100644 > --- a/drivers/net/xen-netback/hash.c > +++ b/drivers/net/xen-netback/hash.c > @@ -51,7 +51,8 @@ static void xenvif_add_hash(struct xenvif *vif, const u8 *tag, > > found = false; > oldest = NULL; > - list_for_each_entry_rcu(entry, &vif->hash.cache.list, link) { > + list_for_each_entry_rcu(entry, &vif->hash.cache.list, link, > + lockdep_is_held(&vif->hash.cache.lock)) { There are probably too many tabs here. Indentation looks wrong. The surrounding code makes it pretty clear that the lock is already held by the time list_for_each_entry_rcu is called, yet the checking involved in lockdep_is_held is not trivial, so I'm afraid I don't consider this a strict improvement over the existing code. If there is something I misunderstood, let me know. Wei. > /* Make sure we don't add duplicate entries */ > if (entry->len == len && > memcmp(entry->tag, tag, len) == 0) > @@ -102,7 +103,8 @@ static void xenvif_flush_hash(struct xenvif *vif) > > spin_lock_irqsave(&vif->hash.cache.lock, flags); > > - list_for_each_entry_rcu(entry, &vif->hash.cache.list, link) { > + list_for_each_entry_rcu(entry, &vif->hash.cache.list, link, > + lockdep_is_held(&vif->hash.cache.lock)) { > list_del_rcu(&entry->link); > vif->hash.cache.count--; > kfree_rcu(entry, rcu); > -- > 2.17.1 >