From 4812f1847a1cb51d0937c3e25eb0db8704d44c4e Mon Sep 17 00:00:00 2001
From: Steffen Klassert <steffen.klassert@secunet.com>
Date: Fri, 2 Jul 2021 09:20:22 +0200
Subject: [PATCH] Revert "xfrm: policy: Read seqcount outside of rcu-read side
 in xfrm_policy_lookup_bytype"

Patch-mainline: v5.14-rc5
Git-commit: eaf228263921cd15962654b539d916380a0f076e
References: bsc#1185675

This reverts commit d7b0408934c749f546b01f2b33d07421a49b6f3e.

This commit tried to fix a locking bug introduced by commit 77cc278f7b20
("xfrm: policy: Use sequence counters with associated lock"). As it
turned out, this patch did not really fix the bug. A proper fix
for this bug is applied on top of this revert.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Varad Gautam <varad.gautam@suse.com>
---
 net/xfrm/xfrm_policy.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 2e1de6b45484..2c28a314c87a 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2097,15 +2097,12 @@ static struct xfrm_policy *xfrm_policy_lookup_bytype(struct net *net, u8 type,
 	if (unlikely(!daddr || !saddr))
 		return NULL;
 
- retry:
-	sequence = read_seqcount_begin(&xfrm_policy_hash_generation);
 	rcu_read_lock();
-
-	chain = policy_hash_direct(net, daddr, saddr, family, dir);
-	if (read_seqcount_retry(&xfrm_policy_hash_generation, sequence)) {
-		rcu_read_unlock();
-		goto retry;
-	}
+ retry:
+	do {
+		sequence = read_seqcount_begin(&xfrm_policy_hash_generation);
+		chain = policy_hash_direct(net, daddr, saddr, family, dir);
+	} while (read_seqcount_retry(&xfrm_policy_hash_generation, sequence));
 
 	ret = NULL;
 	hlist_for_each_entry_rcu(pol, chain, bydst) {
@@ -2136,15 +2133,11 @@ static struct xfrm_policy *xfrm_policy_lookup_bytype(struct net *net, u8 type,
 	}
 
 skip_inexact:
-	if (read_seqcount_retry(&xfrm_policy_hash_generation, sequence)) {
-		rcu_read_unlock();
+	if (read_seqcount_retry(&xfrm_policy_hash_generation, sequence))
 		goto retry;
-	}
 
-	if (ret && !xfrm_pol_hold_rcu(ret)) {
-		rcu_read_unlock();
+	if (ret && !xfrm_pol_hold_rcu(ret))
 		goto retry;
-	}
 fail:
 	rcu_read_unlock();