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>
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@ -117,21 +117,6 @@ static struct entry entries[MAX_ENTRIES];
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static atomic_t overflow_count;
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static atomic_t overflow_count;
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static void reset_entries(void)
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{
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nr_entries = 0;
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memset(entries, 0, sizeof(entries));
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atomic_set(&overflow_count, 0);
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}
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static struct entry *alloc_entry(void)
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{
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if (nr_entries >= MAX_ENTRIES)
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return NULL;
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return entries + nr_entries++;
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}
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/*
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/*
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* The entries are in a hash-table, for fast lookup:
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* The entries are in a hash-table, for fast lookup:
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*/
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*/
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@ -149,6 +134,22 @@ static struct entry *alloc_entry(void)
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static struct entry *tstat_hash_table[TSTAT_HASH_SIZE] __read_mostly;
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static struct entry *tstat_hash_table[TSTAT_HASH_SIZE] __read_mostly;
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static void reset_entries(void)
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{
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nr_entries = 0;
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memset(entries, 0, sizeof(entries));
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memset(tstat_hash_table, 0, sizeof(tstat_hash_table));
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atomic_set(&overflow_count, 0);
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}
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static struct entry *alloc_entry(void)
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{
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if (nr_entries >= MAX_ENTRIES)
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return NULL;
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return entries + nr_entries++;
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}
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static int match_entries(struct entry *entry1, struct entry *entry2)
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static int match_entries(struct entry *entry1, struct entry *entry2)
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{
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{
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return entry1->timer == entry2->timer &&
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return entry1->timer == entry2->timer &&
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@ -202,12 +203,15 @@ static struct entry *tstat_lookup(struct entry *entry, char *comm)
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if (curr) {
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if (curr) {
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*curr = *entry;
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*curr = *entry;
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curr->count = 0;
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curr->count = 0;
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curr->next = NULL;
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memcpy(curr->comm, comm, TASK_COMM_LEN);
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memcpy(curr->comm, comm, TASK_COMM_LEN);
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smp_mb(); /* Ensure that curr is initialized before insert */
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if (prev)
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if (prev)
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prev->next = curr;
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prev->next = curr;
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else
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else
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*head = curr;
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*head = curr;
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curr->next = NULL;
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}
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}
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out_unlock:
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out_unlock:
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spin_unlock(&table_lock);
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spin_unlock(&table_lock);
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@ -360,6 +364,7 @@ static ssize_t tstats_write(struct file *file, const char __user *buf,
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if (!active) {
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if (!active) {
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reset_entries();
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reset_entries();
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time_start = ktime_get();
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time_start = ktime_get();
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smp_mb();
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active = 1;
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active = 1;
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}
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}
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break;
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break;
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