percpu: fix synchronization between synchronous map extension and chunk destruction

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>
Cc: stable@vger.kernel.org # v3.18+
Fixes: 1a4d76076cda ("percpu: implement asynchronous chunk population")

1 files changed, 8 insertions, 8 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
index b1d2a3844792..9903830aaebb 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -162,7 +162,7 @@ static struct pcpu_chunk *pcpu_reserved_chunk;
 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 */
 
@@ -444,6 +444,8 @@ static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc)
         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;
@@ -890,6 +892,9 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
                 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 */
@@ -962,12 +967,9 @@ 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;
                 }
@@ -978,7 +980,6 @@ restart:
                 spin_lock_irqsave(&pcpu_lock, flags);
         }
 
-        mutex_unlock(&pcpu_alloc_mutex);
         goto restart;
 
 area_found:
@@ -988,8 +989,6 @@ 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);
 
@@ -1000,7 +999,6 @@ 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;
@@ -1040,6 +1038,8 @@ 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;
 }