Re: [Xen-devel] linux 4.19 xenstore memory allocation failure Re: [linux-4.19 test] 135420: regressions - FAIL

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Roger Pau Monne writes ("Re: [Xen-devel] linux 4.19 xenstore memory allocation 
failure Re: [linux-4.19 test] 135420: regressions - FAIL"):
> On Tue, Apr 30, 2019 at 03:33:00PM +0100, Ian Jackson wrote:
> > I will leave answering this to the blkfront/linux folks...
> 
> I think those allocations used to be small enough that kcalloc was
> likely fine. Now with multiple rings, and multiple pages per ring
> those have grown to a point where kcalloc is not fine anymore. I will
> prepare a patch to switch to kvcalloc.

Thanks.

FYI this same issue was reported by osstest in
  Subject: [linux-linus test] 135426: regressions - FAIL
ie on linux master.

ISTM that this patch you propose will have to go to stable branches
too ?

> > I would have hoped that it would result in something other than a
> > hang.  At worst, blkfront ought to go into a state where it *knows*
> > that it is utterly broken and reports this properly.
> 
> I haven't yet checked all the possible error paths, but the ones I've
> looked at use xenbus_dev_fatal which switches the device state to
> closing and writes the error message into xenstore.

What if you can't write to xenstore ?  Can we at least have a copy in
the kernel log ?  There might be other errors besides this memory
exhaustion, surely.

Error handling when the usual error reporting path is busted is
difficult indeed, but it is very helpful to have a fallback.

Ian.

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