On Thu, Feb 22, 2018 at 12:51:58PM +0100, Peter Lieven wrote: > Am 22.02.2018 um 12:40 schrieb Daniel P. Berrangé: > > On Thu, Feb 22, 2018 at 12:32:04PM +0100, Kevin Wolf wrote: > >> Am 22.02.2018 um 12:01 hat Peter Lieven geschrieben: > >>> Am 22.02.2018 um 11:57 schrieb Kevin Wolf: > >>>> Am 20.02.2018 um 22:54 hat Paolo Bonzini geschrieben: > >>>>> On 20/02/2018 18:04, Peter Lieven wrote: > >>>>>> Hi, > >>>>>> > >>>>>> I remember we discussed a long time ago to limit the stack usage of all > >>>>>> functions that are executed in a coroutine > >>>>>> context to a very low value to be able to safely limit the coroutine > >>>>>> stack size as well. > >>>>> IIRC the only issue was that hw/ide/atapi.c has mutual recursion between > >>>>> ide_atapi_cmd_reply_end -> ide_transfer_start -> ahci_start_transfer -> > >>>>> ide_atapi_cmd_reply_end. > >>>>> > >>>>> But perhaps it's not an issue, somebody needs to audit the code. > >>>> I think John intended to get rid of the recursion sometime, but I doubt > >>>> he has had the time so far. > >>> Apart from this is is possible to define special cflags in the > >>> Makefile.objs just for a subdirectory? I have patches ready to make > >>> the block layer files and other coroutine users compile with > >>> -Wstack-size=2048. But I do not want to specify each file separately. > >> Our Makefiles have lines like this: > >> > >> iscsi.o-cflags := $(LIBISCSI_CFLAGS) > >> > >> I don't think there is a direct mechanism to apply cflags to a whole > >> directory or just to block-obj-y/block-obj-m, but just looping over them > >> could work. I'm not a Makefile expert at all, but after some toying with > >> a simple example, something like this might work: > >> > >> $(foreach x,$(block-obj-y),$(eval $x-cflags += -Wstack-size=2048)) > > You'll need it for anything block layer depends on too - so that's much > > of util/, crypto/ and io/ directories at least. > > > > So perhaps it would be shorter if we do the opposite - set -Wstack-size=2048 > > globally for everything in QEMU, and then override -Wstack-size=$BIGGER > > for the (hopefully) few sources that have a larger stack need ? > > I tried that already. 2048 is a strong limit for many functions. > It breaks already as soon as some buffer has a size of PATH_MAX, but > thats handleable. But there are some structs around that are very large.
There are surprisingly few "char [PATH_MAX]" variables left in QEMU - we should have a final push to eliminate them regardless. > Generally, it would be a good idea to have a global limit, of course. We could at least put a limit on that matches the current worst case to prevent it getting worse than it already is. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|