From: Ian Jackson Date: Thu, 18 Oct 2012 08:35:02 +0000 (+0100) Subject: libxl: ao: cope with fast ao completion with progess events X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~7724 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=3f6f3a33d8ad1c81c4a0da7524b25762b6ec6bfd;p=xen.git libxl: ao: cope with fast ao completion with progess events There are two egcs in an ao initiator: the one in the AO_CREATE function, and the one in libxl__ao_inprogress. If synchronous ao operation generates progress events and completes immediately, the progress callbacks end up queued in the outer egc. These callbacks are currently only called after libxl__ao_inprogress has returned, and keep the ao alive until they happen. This is not good because the principle is that a synchronous ao is not supposed to survive beyond libxl__ao_inprogress's return. The fix is to ensure that the callbacks queued in the outer egc are called early enough that they don't preserve the ao. This is straightforward in the AO_INPROGRESS macro because AO_CREATE's egc is not used inside that macro other than to destroy it. All we have to do is destroy it a bit sooner. This involves unlocking and relocking the ctx since EGC_FREE expects to be called with the lock released but libxl__ao_inprogress needs it locked. This hole in our lock tenure is fine - libxl__ao_inprogress has such holes already. It is still possible to use the CTX_LOCK macros for this unlock/lock because the gc we are using is destroyed only afterwards by libxl__ao_inprogress. Signed-off-by: Ian Jackson Acked-by: Ian Campbell Committed-by: Ian Campbell --- diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h index 4240ef2b0e..1a221ac544 100644 --- a/tools/libxl/libxl_internal.h +++ b/tools/libxl/libxl_internal.h @@ -1709,10 +1709,12 @@ _hidden void libxl__egc_cleanup(libxl__egc *egc); #define AO_INPROGRESS ({ \ libxl_ctx *ao__ctx = libxl__gc_owner(&ao->gc); \ + CTX_UNLOCK; \ + EGC_FREE; \ + CTX_LOCK; \ int ao__rc = libxl__ao_inprogress(ao, \ __FILE__, __LINE__, __func__); \ libxl__ctx_unlock(ao__ctx); /* gc is now invalid */ \ - EGC_FREE; \ (ao__rc); \ })