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authorBjorn Steinbrink <B.Steinbrink@gmx.de>2007-06-01 00:47:15 -0700
committerChris Wright <chrisw@sous-sol.org>2007-06-11 11:36:48 -0700
commit7434011f268211af4a1e4977f5a1eb2004b1a690 (patch)
tree3e9a5e44c9d50915140f806aacbd5e05d55ca0b8
parent36323d56d52a634758f1288b8a92653b5e6bc1fa (diff)
[PATCH] timer statistics: fix race
Fix two races in the timer stats lookup code. One by ensuring that the initialization of a new entry is finished upon insertion of that entry. The other by cleaning up the hash table when the entries array is cleared, so that we don't have any "pre-inserted" entries. Thanks to Eric Dumazet for reminding me of the memory barriers. Signed-off-by: Bjorn Steinbrink <B.Steinbrink@gmx.de> Signed-off-by: Ian Kumlien <pomac@vapor.com> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Eric Dumazet <dada1@cosmosbay.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Chris Wright <chrisw@sous-sol.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--kernel/time/timer_stats.c37
1 files changed, 21 insertions, 16 deletions
diff --git a/kernel/time/timer_stats.c b/kernel/time/timer_stats.c
index 1bc4882e28e0..e2923eda2576 100644
--- a/kernel/time/timer_stats.c
+++ b/kernel/time/timer_stats.c
@@ -117,21 +117,6 @@ static struct entry entries[MAX_ENTRIES];
static atomic_t overflow_count;
-static void reset_entries(void)
-{
- nr_entries = 0;
- memset(entries, 0, sizeof(entries));
- atomic_set(&overflow_count, 0);
-}
-
-static struct entry *alloc_entry(void)
-{
- if (nr_entries >= MAX_ENTRIES)
- return NULL;
-
- return entries + nr_entries++;
-}
-
/*
* The entries are in a hash-table, for fast lookup:
*/
@@ -149,6 +134,22 @@ static struct entry *alloc_entry(void)
static struct entry *tstat_hash_table[TSTAT_HASH_SIZE] __read_mostly;
+static void reset_entries(void)
+{
+ nr_entries = 0;
+ memset(entries, 0, sizeof(entries));
+ memset(tstat_hash_table, 0, sizeof(tstat_hash_table));
+ atomic_set(&overflow_count, 0);
+}
+
+static struct entry *alloc_entry(void)
+{
+ if (nr_entries >= MAX_ENTRIES)
+ return NULL;
+
+ return entries + nr_entries++;
+}
+
static int match_entries(struct entry *entry1, struct entry *entry2)
{
return entry1->timer == entry2->timer &&
@@ -202,12 +203,15 @@ static struct entry *tstat_lookup(struct entry *entry, char *comm)
if (curr) {
*curr = *entry;
curr->count = 0;
+ curr->next = NULL;
memcpy(curr->comm, comm, TASK_COMM_LEN);
+
+ smp_mb(); /* Ensure that curr is initialized before insert */
+
if (prev)
prev->next = curr;
else
*head = curr;
- curr->next = NULL;
}
out_unlock:
spin_unlock(&table_lock);
@@ -364,6 +368,7 @@ static ssize_t tstats_write(struct file *file, const char __user *buf,
if (!active) {
reset_entries();
time_start = ktime_get();
+ smp_mb();
active = 1;
}
break;