From d9eb706356ad4dbd04aad563ec4d2bcd3d7d6c03 Mon Sep 17 00:00:00 2001 From: Anshul Makkar Date: Tue, 23 May 2017 15:12:58 +0100 Subject: [PATCH] x86/hvmloader: Don't wait for the producer to fill the ring if The condition: if there is a space in the ring then wait for the producer to fill the ring also evaluates to true even if the ring if full. It leads to a deadlock where producer is waiting for consumer to consume the items and consumer is waiting for producer to fill the ring. Fix for the issue: check if the ring is full and then break from the loop to consume the items from the ring. eg. case: prod = 1272, cons = 248. Signed-off-by: Anshul Makkar Reviewed-by: Jan Beulich Release-acked-by: Julien Grall --- tools/firmware/hvmloader/xenbus.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/tools/firmware/hvmloader/xenbus.c b/tools/firmware/hvmloader/xenbus.c index 448157dcb0..2b89a56fce 100644 --- a/tools/firmware/hvmloader/xenbus.c +++ b/tools/firmware/hvmloader/xenbus.c @@ -141,7 +141,19 @@ static void ring_read(char *data, uint32_t len) /* Don't overrun the producer pointer */ while ( (part = MASK_XENSTORE_IDX(rings->rsp_prod - rings->rsp_cons)) == 0 ) + { + /* + * Don't wait for producer to fill the ring if it is already full. + * Condition happens when you write string > 1K into the ring. + * eg case prod=1272 cons=248. + */ + if ( rings->rsp_prod - rings->rsp_cons == XENSTORE_RING_SIZE ) + { + part = XENSTORE_RING_SIZE; + break; + } ring_wait(); + } /* Don't overrun the end of the ring */ if ( part > (XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(rings->rsp_cons)) ) part = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(rings->rsp_cons); -- 2.39.5