[GIT PULL] percpu fixes for 2.6.32-rc6

From: Tejun Heo
Date: Thu Nov 12 2009 - 22:54:16 EST

Hello, Linus.

Please pull from the following percpu fix branch.

git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu.git for-linus

It restructures pcpu_extend_area_map() to de-obfuscate locking and
fixes the following two bugs.

* wrong return value which makes the caller continue walking a
modified list and may lead to oops.

* possible deadlock caused by lock ordering inversion through irq.

Thanks.
---
Tejun Heo (1):
percpu: restructure pcpu_extend_area_map() to fix bugs and improve readability

mm/percpu.c | 121 +++++++++++++++++++++++++++++++++++++++-------------------
1 files changed, 81 insertions(+), 40 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index d907971..5adfc26 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -355,62 +355,86 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
}

/**
- * pcpu_extend_area_map - extend area map for allocation
- * @chunk: target chunk
+ * pcpu_need_to_extend - determine whether chunk area map needs to be extended
+ * @chunk: chunk of interest
*
- * Extend area map of @chunk so that it can accomodate an allocation.
- * A single allocation can split an area into three areas, so this
- * function makes sure that @chunk->map has at least two extra slots.
+ * Determine whether area map of @chunk needs to be extended to
+ * accomodate a new allocation.
*
* CONTEXT:
- * pcpu_alloc_mutex, pcpu_lock. pcpu_lock is released and reacquired
- * if area map is extended.
+ * pcpu_lock.
*
* RETURNS:
- * 0 if noop, 1 if successfully extended, -errno on failure.
+ * New target map allocation length if extension is necessary, 0
+ * otherwise.
*/
-static int pcpu_extend_area_map(struct pcpu_chunk *chunk, unsigned long *flags)
+static int pcpu_need_to_extend(struct pcpu_chunk *chunk)
{
int new_alloc;
- int *new;
- size_t size;

- /* has enough? */
if (chunk->map_alloc >= chunk->map_used + 2)
return 0;

- spin_unlock_irqrestore(&pcpu_lock, *flags);
-
new_alloc = PCPU_DFL_MAP_ALLOC;
while (new_alloc < chunk->map_used + 2)
new_alloc *= 2;

- new = pcpu_mem_alloc(new_alloc * sizeof(new[0]));
- if (!new) {
- spin_lock_irqsave(&pcpu_lock, *flags);
+ return new_alloc;
+}
+
+/**
+ * pcpu_extend_area_map - extend area map of a chunk
+ * @chunk: chunk of interest
+ * @new_alloc: new target allocation length of the area map
+ *
+ * Extend area map of @chunk to have @new_alloc entries.
+ *
+ * CONTEXT:
+ * Does GFP_KERNEL allocation. Grabs and releases pcpu_lock.
+ *
+ * RETURNS:
+ * 0 on success, -errno on failure.
+ */
+static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc)
+{
+ int *old = NULL, *new = NULL;
+ size_t old_size = 0, new_size = new_alloc * sizeof(new[0]);
+ unsigned long flags;
+
+ new = pcpu_mem_alloc(new_size);
+ if (!new)
return -ENOMEM;
- }

- /*
- * Acquire pcpu_lock and switch to new area map. Only free
- * could have happened inbetween, so map_used couldn't have
- * grown.
- */
- spin_lock_irqsave(&pcpu_lock, *flags);
- BUG_ON(new_alloc < chunk->map_used + 2);
+ /* acquire pcpu_lock and switch to new area map */
+ spin_lock_irqsave(&pcpu_lock, flags);
+
+ if (new_alloc <= chunk->map_alloc)
+ goto out_unlock;

- size = chunk->map_alloc * sizeof(chunk->map[0]);
- memcpy(new, chunk->map, size);
+ old_size = chunk->map_alloc * sizeof(chunk->map[0]);
+ memcpy(new, chunk->map, old_size);

/*
* map_alloc < PCPU_DFL_MAP_ALLOC indicates that the chunk is
* one of the first chunks and still using static map.
*/
if (chunk->map_alloc >= PCPU_DFL_MAP_ALLOC)
- pcpu_mem_free(chunk->map, size);
+ old = chunk->map;

chunk->map_alloc = new_alloc;
chunk->map = new;
+ new = NULL;
+
+out_unlock:
+ spin_unlock_irqrestore(&pcpu_lock, flags);
+
+ /*
+ * pcpu_mem_free() might end up calling vfree() which uses
+ * IRQ-unsafe lock and thus can't be called under pcpu_lock.
+ */
+ pcpu_mem_free(old, old_size);
+ pcpu_mem_free(new, new_size);
+
return 0;
}

@@ -1049,7 +1073,7 @@ static void *pcpu_alloc(size_t size, size_t align, bool reserved)
static int warn_limit = 10;
struct pcpu_chunk *chunk;
const char *err;
- int slot, off;
+ int slot, off, new_alloc;
unsigned long flags;

if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {
@@ -1064,14 +1088,25 @@ static void *pcpu_alloc(size_t size, size_t align, bool reserved)
/* serve reserved allocations from the reserved chunk if available */
if (reserved && pcpu_reserved_chunk) {
chunk = pcpu_reserved_chunk;
- if (size > chunk->contig_hint ||
- pcpu_extend_area_map(chunk, &flags) < 0) {
- err = "failed to extend area map of reserved chunk";
+
+ if (size > chunk->contig_hint) {
+ err = "alloc from reserved chunk failed";
goto fail_unlock;
}
+
+ while ((new_alloc = pcpu_need_to_extend(chunk))) {
+ spin_unlock_irqrestore(&pcpu_lock, flags);
+ if (pcpu_extend_area_map(chunk, new_alloc) < 0) {
+ err = "failed to extend area map of reserved chunk";
+ goto fail_unlock_mutex;
+ }
+ spin_lock_irqsave(&pcpu_lock, flags);
+ }
+
off = pcpu_alloc_area(chunk, size, align);
if (off >= 0)
goto area_found;
+
err = "alloc from reserved chunk failed";
goto fail_unlock;
}
@@ -1083,14 +1118,20 @@ restart:
if (size > chunk->contig_hint)
continue;

- switch (pcpu_extend_area_map(chunk, &flags)) {
- case 0:
- break;
- case 1:
- goto restart; /* pcpu_lock dropped, restart */
- default:
- err = "failed to extend area map";
- goto fail_unlock;
+ new_alloc = pcpu_need_to_extend(chunk);
+ if (new_alloc) {
+ spin_unlock_irqrestore(&pcpu_lock, flags);
+ if (pcpu_extend_area_map(chunk,
+ new_alloc) < 0) {
+ err = "failed to extend area map";
+ goto fail_unlock_mutex;
+ }
+ spin_lock_irqsave(&pcpu_lock, flags);
+ /*
+ * pcpu_lock has been dropped, need to
+ * restart cpu_slot list walking.
+ */
+ goto restart;
}

off = pcpu_alloc_area(chunk, size, align);

--
tejun
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/