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client-ip=162.221.158.21; receiver=esa2.hc3370-68.iphmx.com; envelope-from="Ian.Jackson@citrix.com"; x-sender="postmaster@mail.citrix.com"; x-conformance=sidf_compatible IronPort-SDR: /3Y4gLvuy/92Dv4CGu/0cx1Ik2zFrx69pbn95ugEw5OTYP/7WKyqVo+XFYI4efRG3J9xzvpLh7 vhvgDArV4WQ3UqsyQnKKF5PZK3bI5A5kKZuiur0MMfC8KDmh0pgvyPSw/7MuPi+mrW29F+yuj6 g6ZFNce3XbidnvL96GPs1YBk5lYyOyYwTfaEZaRk+cwD7JUq1FGB3v+o6FVYZwmVkBKS8ixM7I i376A+XKAwmMty8hXVGlxf+JlVB1uGf+spGbEfBdhwy4NoDHxqCIJMblSyFYl+uqbJqdwG7Txy XOI= X-SBRS: 2.7 X-MesageID: 10756446 X-Ironport-Server: esa2.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.69,417,1571716800"; d="scan'208";a="10756446" From: Ian Jackson To: Date: Fri, 10 Jan 2020 13:29:01 +0000 Message-ID: <20200110132902.29295-8-ian.jackson@eu.citrix.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20200110132902.29295-1-ian.jackson@eu.citrix.com> References: <20200110132902.29295-1-ian.jackson@eu.citrix.com> MIME-Version: 1.0 Subject: [Xen-devel] [PATCH 7/8] libxl: event: Fix possible hang with libxl_osevent_beforepoll X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Anthony PERARD , Ian Jackson , George Dunlap , Wei Liu Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" If the application uses libxl_osevent_beforepoll, a similar hang is possible to the one described and fixed in libxl: event: Fix hang when mixing blocking and eventy calls Application behaviour would have to be fairly unusual, but it doesn't seem sensible to just leave this latent bug. We fix the latent bug by waking up the "poller_app" pipe every time we add osevents. If the application does not ever call beforepoll, we write one byte to the pipe and set pipe_nonempty and then we ignore it. We only write another byte if beforepoll is called again. Normally in an eventy program there would only be one thread calling libxl_osevent_beforepoll. The effect in such a program is to sometimes needlessly go round the poll loop again if a timeout callback becomes interested in a new osevent. We'll fix that in a moment. Signed-off-by: Ian Jackson --- tools/libxl/libxl_event.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c index 4d57843cce..4314191c3b 100644 --- a/tools/libxl/libxl_event.c +++ b/tools/libxl/libxl_event.c @@ -59,6 +59,9 @@ void libxl__egc_cleanup_1_baton(libxl__egc *egc) EGC_GC; libxl__poller *search, *wake=0; + if (CTX->poller_app->osevents_added) + baton_wake(egc, CTX->poller_app); + LIBXL_LIST_FOREACH(search, &CTX->pollers_active, active_entry) { if (search == CTX->poller_app) /* This one is special. We can't give it the baton. */