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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, May 01, 2019 at 10:47:49AM +0100, Ian Jackson wrote:
> 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 agree.

> > > 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.

There's a call to dev_err also, which should print the same error
that's written to xenstore on the console. That however requires the
memory allocation of page in order to format the string to be printed
(see xenbus_va_dev_error).

Roger.

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