linux-kernel - [PATCH] [RFC] CFQ: simplify radix tree lookup in cfq_cic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <1312402472.22854.16.camel@t41.thuisdomein>
Date:	Wed, 03 Aug 2011 22:14:32 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] [RFC] CFQ: simplify radix tree lookup in cfq_cic_lookup()

0) Not tested and not signed-off.

1) This is to see whether I understand the cfqd->cic_index usage (at
least, part of it).

2) If the lookup of a cic in the radix tree turned up a "dead" cic, then
that cic will be dropped. There's no reason to again try to lookup that
cic: that lookup should return NULL. (If it doesn't return NULL, we seem
to be in trouble.) So there's no need for a do {[...]} while (1) loop
and this code can be simplified a little.

3) Does this make sense?


Paul Bolle
---
 block/cfq-iosched.c |   28 +++++++++++++---------------
 1 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 1f96ad6..0d33d8c 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3120,22 +3120,20 @@ cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
 		return cic;
 	}
 
-	do {
-		cic = radix_tree_lookup(&ioc->radix_root, cfqd->cic_index);
-		rcu_read_unlock();
-		if (!cic)
-			break;
-		if (unlikely(cic->key != cfqd)) {
-			cfq_drop_dead_cic(cfqd, ioc, cic);
-			rcu_read_lock();
-			continue;
-		}
+	cic = radix_tree_lookup(&ioc->radix_root, cfqd->cic_index);
+	rcu_read_unlock();
 
-		spin_lock_irqsave(&ioc->lock, flags);
-		rcu_assign_pointer(ioc->ioc_data, cic);
-		spin_unlock_irqrestore(&ioc->lock, flags);
-		break;
-	} while (1);
+	if (!cic)
+		return NULL;
+
+	if (unlikely(cic->key != cfqd)) {
+		cfq_drop_dead_cic(cfqd, ioc, cic);
+		return NULL;
+	}
+
+	spin_lock_irqsave(&ioc->lock, flags);
+	rcu_assign_pointer(ioc->ioc_data, cic);
+	spin_unlock_irqrestore(&ioc->lock, flags);
 
 	return cic;
 }
-- 
1.7.6

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/