>From ed528d05b7800d651ef5e36de37732a06b456462 Mon Sep 17 00:00:00 2001
From: Akira Yokosawa <akiyks@xxxxxxxxx>
Date: Sat, 5 Jan 2019 00:15:47 +0900
Subject: [PATCH 2/2] datastruct/hash: Annotate racy accesses with READ_ONCE/WRITE_ONCE
ht_get_bucket() runs concurrently with hash_resize().
As a defensive coding rule to survive compiler optimization,
accesses to (*htp)->ht_resize_cur, (*htp)->ht_new, and
(*htp)->ht_idx should be annotated by READ_ONCE/WRITE_ONCE.
Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx>
---
CodeSamples/datastruct/hash/hash_resize.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/CodeSamples/datastruct/hash/hash_resize.c b/CodeSamples/datastruct/hash/hash_resize.c
index 57c75c1..e1d92a6 100644
--- a/CodeSamples/datastruct/hash/hash_resize.c
+++ b/CodeSamples/datastruct/hash/hash_resize.c
@@ -137,13 +137,13 @@ ht_get_bucket(struct ht **htp, void *key, long *b, int *i)
htbp = ht_get_bucket_single(*htp, key, b); //\lnlbl{call_single}
//\fcvexclude
- if (*b <= (*htp)->ht_resize_cur) { //\lnlbl{resized}
+ if (*b <= READ_ONCE((*htp)->ht_resize_cur)) { //\lnlbl{resized}
smp_mb(); /* order ->ht_resize_cur before ->ht_new. */
- *htp = (*htp)->ht_new; //\lnlbl{newtable}
+ *htp = READ_ONCE((*htp)->ht_new); //\lnlbl{newtable}
htbp = ht_get_bucket_single(*htp, key, b); //\lnlbl{newbucket}
}
if (i) //\lnlbl{chk_i}
- *i = (*htp)->ht_idx; //\lnlbl{set_idx}
+ *i = READ_ONCE((*htp)->ht_idx); //\lnlbl{set_idx}
return htbp; //\lnlbl{return}
} //\lnlbl{e}
//\end{snippet}
@@ -301,10 +301,10 @@ int hashtab_resize(struct hashtab *htp_master,
spin_unlock(&htp_master->ht_lock); //\lnlbl{rel_nomem}
return -ENOMEM; //\lnlbl{ret_nomem}
}
- htp->ht_new = htp_new; //\lnlbl{set_newtbl}
+ WRITE_ONCE(htp->ht_new, htp_new); //\lnlbl{set_newtbl}
synchronize_rcu(); //\lnlbl{sync_rcu}
idx = htp->ht_idx; //\lnlbl{get_curidx}
- htp_new->ht_idx = !idx;
+ WRITE_ONCE(htp_new->ht_idx, !idx);
for (i = 0; i < htp->ht_nbuckets; i++) { //\lnlbl{loop:b}
htbp = &htp->ht_bkt[i]; //\lnlbl{get_oldcur}
spin_lock(&htbp->htb_lock); //\lnlbl{acq_oldcur}
@@ -315,7 +315,7 @@ int hashtab_resize(struct hashtab *htp_master,
spin_unlock(&htbp_new->htb_lock);
} //\lnlbl{loop_list:e}
smp_mb(); /* Fill new buckets before claiming them. */
- htp->ht_resize_cur = i; //\lnlbl{update_resize}
+ WRITE_ONCE(htp->ht_resize_cur, i); //\lnlbl{update_resize}
spin_unlock(&htbp->htb_lock); //\lnlbl{rel_oldcur}
} //\lnlbl{loop:e}
rcu_assign_pointer(htp_master->ht_cur, htp_new); //\lnlbl{rcu_assign}
--
2.7.4
