Date: Thu, 15 Oct 2020 11:44:28 +0000 (UTC) From: Wei Hu <whu@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r366721 - head/sys/dev/hyperv/netvsc Message-ID: <202010151144.09FBiSNV088172@repo.freebsd.org>
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Author: whu Date: Thu Oct 15 11:44:28 2020 New Revision: 366721 URL: https://svnweb.freebsd.org/changeset/base/366721 Log: 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 Modified: head/sys/dev/hyperv/netvsc/if_hn.c Modified: head/sys/dev/hyperv/netvsc/if_hn.c ============================================================================== --- head/sys/dev/hyperv/netvsc/if_hn.c Thu Oct 15 05:57:20 2020 (r366720) +++ head/sys/dev/hyperv/netvsc/if_hn.c Thu Oct 15 11:44:28 2020 (r366721) @@ -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)
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