From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Accesses to slab_index are protected by slab_lock everywhere except
in a sanity check in stack_depot_fetch. The read access there can race
with the write access in depot_alloc_stack.
Use WRITE/READ_ONCE() to annotate the racy accesses.
As the sanity check is only used to print a warning in case of a
violation of the stack depot interface usage, it does not make a lot
of sense to use proper synchronization.
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
lib/stackdepot.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index f291ad6a4e72..cc2fe8563af4 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -269,8 +269,11 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
return NULL;
}
- /* Move on to the next slab. */
- slab_index++;
+ /*
+ * Move on to the next slab.
+ * WRITE_ONCE annotates a race with stack_depot_fetch.
+ */
+ WRITE_ONCE(slab_index, slab_index + 1);
slab_offset = 0;
/*
* smp_store_release() here pairs with smp_load_acquire() in
@@ -492,6 +495,8 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
unsigned long **entries)
{
union handle_parts parts = { .handle = handle };
+ /* READ_ONCE annotates a race with depot_alloc_stack. */
+ int slab_index_cached = READ_ONCE(slab_index);
void *slab;
size_t offset = parts.offset << DEPOT_STACK_ALIGN;
struct stack_record *stack;
@@ -500,9 +505,9 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
if (!handle)
return 0;
- if (parts.slab_index > slab_index) {
+ if (parts.slab_index > slab_index_cached) {
WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
- parts.slab_index, slab_index, handle);
+ parts.slab_index, slab_index_cached, handle);
return 0;
}
slab = stack_slabs[parts.slab_index];
--
2.25.1
