From d9a5cb291c733a31a968ac145f622b687ddd1c66 Mon Sep 17 00:00:00 2001
From: Tri Dao <tridpq@gmail.com>
Date: Sat, 10 Feb 2024 01:03:00 -0800
Subject: [PATCH] Fix dv = torch::empty_like(k) for mha_bwd_varlen as well

---
 csrc/flash_attn/flash_api.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/csrc/flash_attn/flash_api.cpp b/csrc/flash_attn/flash_api.cpp
index 80dd5a3..2288850 100644
--- a/csrc/flash_attn/flash_api.cpp
+++ b/csrc/flash_attn/flash_api.cpp
@@ -1069,7 +1069,7 @@ mha_varlen_bwd(const at::Tensor &dout,  // total_q x num_heads, x head_size
         TORCH_CHECK(dv.stride(-1) == 1, "dv must have contiguous last dimension");
         CHECK_SHAPE(dv, total_k, num_heads_k, head_size);
     } else {
-        dv = torch::empty_like(k);
+        dv = torch::empty_like(v);
     }
 
     at::Tensor dout_padded;