In the case the user-space daemon crashes, hangs or is killed, we
need to down the semaphore, otherwise, after the daemon starts next
time, the obsolete data in fcopy_transaction.message or
fcopy_transaction.fcopy_msg will be used immediately.
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
---
v2: I removed the "FCP" prefix as Greg asked.
I also updated the output message a little:
"FCP: failed to acquire the semaphore" -->
"can not acquire the semaphore: it is benign"
v3: I added the code in fcopy_release() as Jason Wang suggested.
I removed the pr_debug (it isn't so meaningful)and added a comment instead.
v4: this is a resend of v3, plus adding a comment before
fcopy_release().
---
drivers/hv/hv_fcopy.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
index 23b2ce2..cd453e4 100644
--- a/drivers/hv/hv_fcopy.c
+++ b/drivers/hv/hv_fcopy.c
@@ -86,6 +86,18 @@ static void fcopy_work_func(struct work_struct *dummy)
* process the pending transaction.
*/
fcopy_respond_to_host(HV_E_FAIL);
+
+ /* In the case the user-space daemon crashes, hangs or is killed, we
+ * need to down the semaphore, otherwise, after the daemon starts next
+ * time, the obsolete data in fcopy_transaction.message or
+ * fcopy_transaction.fcopy_msg will be used immediately.
+ *
+ * NOTE: fcopy_read() happens to get the semaphore (very rare)? We're
+ * still OK, because we've reported the failure to the host.
+ */
+ if (down_trylock(&fcopy_transaction.read_sema))
+ ;
+
}
static int fcopy_handle_handshake(u32 version)
@@ -344,6 +356,14 @@ static int fcopy_open(struct inode *inode, struct file *f)
return 0;
}
+/* XXX: there are still some tricky corner cases, e.g.,
+ * 1) In a SMP guest, when fcopy_release() runs between
+ * schedule_delayed_work() and fcopy_send_data(), there is
+ * still a chance an obsolete message will be queued.
+ *
+ * 2) When the fcopy daemon is running, if we unload the driver,
+ * we'll notice a kernel oops when we kill the daemon later.
+ */
static int fcopy_release(struct inode *inode, struct file *f)
{
/*
@@ -351,6 +371,13 @@ static int fcopy_release(struct inode *inode, struct file *f)
*/
in_hand_shake = true;
opened = false;
+
+ if (cancel_delayed_work_sync(&fcopy_work)) {
+ /* We haven't up()-ed the semaphore(very rare)? */
+ if (down_trylock(&fcopy_transaction.read_sema))
+ ;
+ fcopy_respond_to_host(HV_E_FAIL);
+ }
return 0;
}
--
1.9.1
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