Re: [Xen-devel] [PATCH 1/2] build system: make install-stubdom depend on install-tools again

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Apr 15, 2019 at 05:28:08PM +0100, Ian Jackson wrote:
> In d290e325179ccee966cd679d0fed48be6f4cc1b7
>   "build system: don't let install-stubdom depend on install-tools"
> the dependency of install-stubdom on install-tools was removed.
> 
> However, this was not correct.   stubdom/Makefile contains this:
> 
>   $(XEN_ROOT)/tools/qemu-xen-traditional-dir:
>        $(MAKE) DESTDIR= -C $(XEN_ROOT)/tools qemu-xen-traditional-dir-find
> 
> As I have written before:
> 
>   With recursive make, it is necessary for the overall structure of the
>   makefiles to sequence things so that each directory is entered exactly
>   once, before its dependent directories are entered.  (It is possible
>   to violate this rule without creating races but it is tricky and
>   inadvisable.)
> 
> Since d290e325179c, it can happen that the command for the
> qemu-xen-traditional-dir-find rule is run twice simultaneously - once
> as a result of $(MAKE) -C tools install, and once as a result of
> $(MAKE) -C stubdom install.  If you get unlucky, this causes lossage.
> (This just happened to me in an osstest flight.)
> 
> In principle we could alternatively fix this by lifting the commands
> in the qemu-xen-traditional-dir-find target (and perhaps other things
> too) into the toplevel Makefile, as was done for mini-os.
> 
> But that seems overkill given how bad the stubdom build system is, and
> the fact that we think at some point this qemu-trad will go away
> entirely.  Adding the tools dependency back to the stubdom build is
> by and large good enough.
> 
> (Someone who really wants to build stubdom without tools is welcome to
> do this separation if they really want to.)
> 
> CC: Juergen Gross <jgross@xxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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