[PATCH v2 2/2] nbd: add comments about double lock for config_lock confusion
From: Xiubo Li <xiubli@redhat.com>
When calling the ioctl(), fget() will be called on this fd, and
nbd_release() is only called when the fd's refcount drops to zero.
With this we can make sure that the nbd_release() won't be called
before the ioctl() finished.
So there won't have the double lock issue for the "config_lock",
which has already been held by nbd_ioctl().
Signed-off-by: Xiubo Li <xiubli@redhat.com>
---
drivers/block/nbd.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 3bb8281bb753..48f36b003bf5 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1345,6 +1345,17 @@ static void nbd_clear_sock_ioctl(struct nbd_device *nbd,
sock_shutdown(nbd);
__invalidate_device(bdev, true);
nbd_bdev_reset(bdev);
+
+ /*
+ * When calling the ioctl(), fget() will be called on this
+ * fd, and nbd_release() is only called when the fd's refcount
+ * drops to zero. With this we can make sure that the
+ * nbd_release() won't be called before the ioctl() finished.
+ *
+ * So there won't have the double lock issue if it will
+ * call the nbd_config_put() here for the "config_lock", which
+ * has already been held by nbd_ioctl().
+ */
if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
&nbd->config->runtime_flags))
nbd_config_put(nbd);
--
2.18.4
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