Re: [libvirt] [PATCH] Document that ff callbacks need to be invoked from a clean stack

On Tue, Aug 16, 2011 at 02:24:53PM +0200, Guido Günther wrote: > Hi Daniel, > On Sat, Aug 13, 2011 at 08:57:45PM -0700, Daniel P. Berrange wrote: > > On Fri, Aug 12, 2011 at 11:54:28PM +0200, Guido Günther wrote: > [..snip..] > > In the default libvirt event loop, the 'ff' callback is always invoked > > from a "clean" stack in the event loop, so you never have this problem > > with re-entrancy. > > > > > Working around this by removing the locks from > > > virNetSocketRemoveIOCallback leads to another deadlock: > > > > Yeah this is not a viable approach. > Sure. This was only to see what else fails. > > > > > > > I didn't see a simple way to fix this but would welcome any suggestions. > > > > IMHO we just have to document that event loop implementations > > should make sure that the 'ff' callbacks are always invoked > > from a clean stack. In the case of virt-viewer, this means > > changing it to register a g_idle callback function to invoke > > the 'ff' callback. > > Patch for virt-viewer attached. I'll come up with a doc patch for > libvirt once I have a bit more time. As promised here's the patch for libvirt. O.k. to apply? Cheers, -- Guido

From c2e2be4e377871ace12bb7adfde130e9b8779ab5 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Guido=20G=C3=BCnther?= <agx(a)sigxcpu.org&gt; Date: Mon, 3 Oct 2011 22:24:13 +0200 Subject: [PATCH] Document that ff callbacks need to be invoked from a clean stack. --- include/libvirt/libvirt.h.in | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-) diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in index a3c581d..bd7a0f7 100644 --- a/include/libvirt/libvirt.h.in +++ b/include/libvirt/libvirt.h.in @@ -2243,13 +2243,15 @@ typedef void (*virEventHandleCallback)(int watch, int fd, int events, void *opaq * @opaque: user data to pass to the callback * @ff: the callback invoked to free opaque data blob * - * Part of the EventImpl, this callback Adds a file handle callback to + * Part of the EventImpl, this callback adds a file handle callback to * listen for specific events. The same file handle can be registered * multiple times provided the requested event sets are non-overlapping * * If the opaque user data requires free'ing when the handle * is unregistered, then a 2nd callback can be supplied for - * this purpose. + * this purpose. This callback needs to be invoked from a clean stack. + * If 'ff' callbacks are invoked directly from the virEventRemoveHandleFunc + * they will likely deadlock in libvirt. * * Returns a handle watch number to be used for updating * and unregistering for events