vhost: make page logging atomic

Each dirty page logging operation should be atomic. But it's not
atomic in current implementation. So it's possible that some dirty
pages can't be logged successfully when different threads try to
log different pages into the same byte of the log buffer concurrently.
This patch fixes this issue.

Fixes: b171fad1ffa5 ("vhost: log used vring changes")
Cc: stable@dpdk.org
Reported-by: Xiao Wang <xiao.w.wang@intel.com>
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 0f294f39596ff9f7f29e67ed0f5500da3ed02035..6fe72aeb61df2ac977c633f46a4d425aa7294e2c 100644 (file)
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -201,10 +201,19 @@ struct virtio_net {
 
 #define VHOST_LOG_PAGE 4096
 
+/*
+ * Atomically set a bit in memory.
+ */
+static __rte_always_inline void
+vhost_set_bit(unsigned int nr, volatile uint8_t *addr)
+{
+       __sync_fetch_and_or_8(addr, (1U << nr));
+}
+
 static __rte_always_inline void
 vhost_log_page(uint8_t *log_base, uint64_t page)
 {
-       log_base[page / 8] |= 1 << (page % 8);
+       vhost_set_bit(page % 8, &log_base[page / 8]);
 }
 
 static __rte_always_inline void