[PATCH 4.4 067/146] percpu: fix synchronization between synchronous map extension and chunk destruction

Greg Kroah-Hartman
2016-07-25T22:42:36Z

From: Tejun Heo <tj@kernel.org>

commit 6710e594f71ccaad8101bc64321152af7cd9ea28 upstream.

For non-atomic allocations, pcpu_alloc() can try to extend the area
map synchronously after dropping pcpu_lock; however, the extension
wasn't synchronized against chunk destruction and the chunk might get
freed while extension is in progress.

This patch fixes the bug by putting most of non-atomic allocations
under pcpu_alloc_mutex to synchronize against pcpu_balance_work which
is responsible for async chunk management including destruction.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-and-tested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Fixes: 1a4d76076cda ("percpu: implement asynchronous chunk population")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/percpu.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -160,7 +160,7 @@ static struct pcpu_chunk *pcpu_reserved_
static int pcpu_reserved_chunk_limit;

static DEFINE_SPINLOCK(pcpu_lock); /* all internal data structures */
-static DEFINE_MUTEX(pcpu_alloc_mutex); /* chunk create/destroy, [de]pop */
+static DEFINE_MUTEX(pcpu_alloc_mutex); /* chunk create/destroy, [de]pop, map ext */

static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */

@@ -446,6 +446,8 @@ static int pcpu_extend_area_map(struct p
size_t old_size = 0, new_size = new_alloc * sizeof(new[0]);
unsigned long flags;

+ lockdep_assert_held(&pcpu_alloc_mutex);
+
new = pcpu_mem_zalloc(new_size);
if (!new)
return -ENOMEM;
@@ -892,6 +894,9 @@ static void __percpu *pcpu_alloc(size_t
return NULL;
}

+ if (!is_atomic)
+ mutex_lock(&pcpu_alloc_mutex);
+
spin_lock_irqsave(&pcpu_lock, flags);

/* serve reserved allocations from the reserved chunk if available */
@@ -964,12 +969,9 @@ restart:
if (is_atomic)
goto fail;

- mutex_lock(&pcpu_alloc_mutex);
-
if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) {
chunk = pcpu_create_chunk();
if (!chunk) {
- mutex_unlock(&pcpu_alloc_mutex);
err = "failed to allocate new chunk";
goto fail;
}
@@ -980,7 +982,6 @@ restart:
spin_lock_irqsave(&pcpu_lock, flags);
}

- mutex_unlock(&pcpu_alloc_mutex);
goto restart;

area_found:
@@ -990,8 +991,6 @@ area_found:
if (!is_atomic) {
int page_start, page_end, rs, re;

- mutex_lock(&pcpu_alloc_mutex);
-
page_start = PFN_DOWN(off);
page_end = PFN_UP(off + size);

@@ -1002,7 +1001,6 @@ area_found:

spin_lock_irqsave(&pcpu_lock, flags);
if (ret) {
- mutex_unlock(&pcpu_alloc_mutex);
pcpu_free_area(chunk, off, &occ_pages);
err = "failed to populate";
goto fail_unlock;
@@ -1042,6 +1040,8 @@ fail:
/* see the flag handling in pcpu_blance_workfn() */
pcpu_atomic_alloc_failed = true;
pcpu_schedule_balance_work();
+ } else {
+ mutex_unlock(&pcpu_alloc_mutex);
}
return NULL;
}