Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 9fcc15ec authored by Björn Steinbrink's avatar Björn Steinbrink Committed by Linus Torvalds
Browse files

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: default avatarBjorn Steinbrink <B.Steinbrink@gmx.de>
Signed-off-by: default avatarIan Kumlien <pomac@vapor.com>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c79d9c9e

kernel/time/timer_stats.c

+21 −16
Original line number Diff line number Diff line
@@ -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);
@@ -360,6 +364,7 @@ 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;