[libvirt] [PATCH] Fix errno check, prevent spurious errors under heavy load
From man poll(2), poll does not set errno=EAGAIN, however it does set errno=EINTR. Have libvirt retry on the appropriate errno.
Under heavy load, a program of mine kept getting libvirt errors 'poll on socket failed: Interrupted system call'. The signals were SIGCHLD from processes forked by threads unrelated to those using libvirt. diff --git a/src/rpc/virnetclient.c b/src/rpc/virnetclient.c index 2530ffa..f2a6922 100644 --- a/src/rpc/virnetclient.c +++ b/src/rpc/virnetclient.c @@ -1374,7 +1374,7 @@ static int virNetClientIOEventLoop(virNetClientPtr client, repoll: ret = poll(fds, ARRAY_CARDINALITY(fds), timeout); - if (ret < 0 && errno == EAGAIN) + if (ret < 0 && errno == EINTR) goto repoll; ignore_value(pthread_sigmask(SIG_SETMASK, &oldmask, NULL));
On 08/08/2012 02:59 PM, Peter Feiner wrote:
From man poll(2), poll does not set errno=EAGAIN, however it does set errno=EINTR. Have libvirt retry on the appropriate errno.
man poll(2) is slightly wrong - according to POSIX, poll may _also_ set EAGAIN when "The allocation of internal data structures failed but a subsequent request may succeed." But you are correct that poll() interrupted by a signal must be EINTR. I went looking (git grep -A3 '\bpoll *([a-zA-Z]'), and some of our code already checks for _both_ EAGAIN and EINTR, so I'd feel safer updating ALL the code to check for both instead of one.
Under heavy load, a program of mine kept getting libvirt errors 'poll on socket failed: Interrupted system call'. The signals were SIGCHLD from processes forked by threads unrelated to those using libvirt.
diff --git a/src/rpc/virnetclient.c b/src/rpc/virnetclient.c index 2530ffa..f2a6922 100644 --- a/src/rpc/virnetclient.c +++ b/src/rpc/virnetclient.c @@ -1374,7 +1374,7 @@ static int virNetClientIOEventLoop(virNetClientPtr client,
repoll: ret = poll(fds, ARRAY_CARDINALITY(fds), timeout); - if (ret < 0 && errno == EAGAIN) + if (ret < 0 && errno == EINTR) goto repoll;
ignore_value(pthread_sigmask(SIG_SETMASK, &oldmask, NULL));
I squashed this into your change, and pushed. I also added you to AUTHORS; let me know if you prefer an alternate spelling of name or email. diff --git i/src/rpc/virnetclient.c w/src/rpc/virnetclient.c index 2530ffa..42bdc54 100644 --- i/src/rpc/virnetclient.c +++ w/src/rpc/virnetclient.c @@ -1,7 +1,7 @@ /* * virnetclient.c: generic network RPC client * - * Copyright (C) 2006-2011 Red Hat, Inc. + * Copyright (C) 2006-2012 Red Hat, Inc. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public @@ -651,7 +651,7 @@ int virNetClientSetTLSSession(virNetClientPtr client, repoll: ret = poll(fds, ARRAY_CARDINALITY(fds), -1); - if (ret < 0 && errno == EAGAIN) + if (ret < 0 && (errno == EAGAIN || errno == EINTR)) goto repoll; ignore_value(pthread_sigmask(SIG_BLOCK, &oldmask, NULL)); @@ -675,7 +675,7 @@ int virNetClientSetTLSSession(virNetClientPtr client, repoll2: ret = poll(fds, ARRAY_CARDINALITY(fds), -1); - if (ret < 0 && errno == EAGAIN) + if (ret < 0 && (errno == EAGAIN || errno == EINTR)) goto repoll2; ignore_value(pthread_sigmask(SIG_BLOCK, &oldmask, NULL)); @@ -1374,7 +1374,7 @@ static int virNetClientIOEventLoop(virNetClientPtr client, repoll: ret = poll(fds, ARRAY_CARDINALITY(fds), timeout); - if (ret < 0 && errno == EAGAIN) + if (ret < 0 && (errno == EAGAIN || errno == EINTR)) goto repoll; ignore_value(pthread_sigmask(SIG_SETMASK, &oldmask, NULL)); diff --git i/src/util/event_poll.c w/src/util/event_poll.c index 1bc1d41..0e7d1c1 100644 --- i/src/util/event_poll.c +++ w/src/util/event_poll.c @@ -1,7 +1,7 @@ /* * event.c: event loop for monitoring file handles * - * Copyright (C) 2007, 2010-2011 Red Hat, Inc. + * Copyright (C) 2007, 2010-2012 Red Hat, Inc. * Copyright (C) 2007 Daniel P. Berrange * * This library is free software; you can redistribute it and/or @@ -615,7 +615,7 @@ int virEventPollRunOnce(void) { ret = poll(fds, nfds, timeout); if (ret < 0) { EVENT_DEBUG("Poll got error event %d", errno); - if (errno == EINTR) { + if (errno == EINTR || errno == EAGAIN) { goto retry; } virReportSystemError(errno, "%s", -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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Eric Blake -
Peter Feiner