git: 70f7b2475333 - stable/12 - Hyper-V: hn: Relinquish cpu in HN_LOCK to avoid deadlock

[Wei Hu]

The branch stable/12 has been updated by whu:

URL: https://cgit.FreeBSD.org/src/commit/?id=70f7b24753336efeb3cf6e73040780b2e4d28d8a

commit 70f7b24753336efeb3cf6e73040780b2e4d28d8a
Author:     Wei Hu <whu at FreeBSD.org>
AuthorDate: 2020-10-15 11:44:28 +0000
Commit:     Wei Hu <whu at FreeBSD.org>
CommitDate: 2021-03-15 05:15:21 +0000

    Hyper-V: hn: Relinquish cpu in HN_LOCK to avoid deadlock
    
    The try lock loop in HN_LOCK put the thread spinning on cpu if the lock
    is not available. It is possible to cause deadlock if the thread holding
    the lock is sleeping. Relinquish the cpu to work around this problem even
    it doesn't completely solve the issue. The priority inversion could cause
    the livelock no matter how less likely it could happen. A more complete
    solution may be needed in the future.
    
    Reported by:    Microsoft, Netapp
    MFC after:      2 weeks
    Sponsored by:   Microsoft
    
    (cherry picked from commit b3460f44524b145c6c8a760ebe65052560a810bf)
---
 sys/dev/hyperv/netvsc/if_hn.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/sys/dev/hyperv/netvsc/if_hn.c b/sys/dev/hyperv/netvsc/if_hn.c
index e9d1b9439671..1945732590cc 100644
--- a/sys/dev/hyperv/netvsc/if_hn.c
+++ b/sys/dev/hyperv/netvsc/if_hn.c
@@ -71,8 +71,10 @@ __FBSDID("$FreeBSD$");
 #include <sys/module.h>
 #include <sys/queue.h>
 #include <sys/lock.h>
+#include <sys/proc.h>
 #include <sys/rmlock.h>
 #include <sys/sbuf.h>
+#include <sys/sched.h>
 #include <sys/smp.h>
 #include <sys/socket.h>
 #include <sys/sockio.h>
@@ -165,8 +167,11 @@ __FBSDID("$FreeBSD$");
 #define HN_LOCK_ASSERT(sc)		sx_assert(&(sc)->hn_lock, SA_XLOCKED)
 #define HN_LOCK(sc)					\
 do {							\
-	while (sx_try_xlock(&(sc)->hn_lock) == 0)	\
+	while (sx_try_xlock(&(sc)->hn_lock) == 0) {	\
+		/* Relinquish cpu to avoid deadlock */	\
+		sched_relinquish(curthread);		\
 		DELAY(1000);				\
+	}						\
 } while (0)
 #define HN_UNLOCK(sc)			sx_xunlock(&(sc)->hn_lock)