On Thu, Apr 4, 2019 at 4:09 PM Christian Brauner christian@brauner.io wrote:

On Wed, Apr 03, 2019 at 07:08:47PM +0200, Matteo Croce wrote:

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On Wed, Apr 3, 2019 at 6:40 PM Matteo Croce mcroce@redhat.com wrote:

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On Wed, Apr 3, 2019 at 5:51 PM Matthew Wilcox willy@infradead.org wrote:

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On Wed, Apr 03, 2019 at 05:24:26PM +0200, Matteo Croce wrote:

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On Wed, Apr 3, 2019 at 4:02 PM Christian Brauner christian@brauner.io wrote:

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Yeah, maybe but it still feels cleaner and more obvious to just add:

static long long_zero;

given that most callers actually seem to want an (unsigned) int.

I don't have a strong opinion though so if others feel that it's just a waste of space consider it acked.

Well, given that the value is zero, in this expectional case we could avoid duplicating the symbol and save 4 bytes. What the maintainers think?

If we care about saving four bytes, we could just pass the address of ZERO_PAGE(0).

That would work, work too, maybe it's a bit overkill. int zero is always there and it's static, so enlarging it to long should be a straightforward fix. Obviously we can't do it for other numbers, but we can alias it just for the zero case..

Regards,

-- Matteo Croce per aspera ad upstream

Anyway, I'm fine with both solutions, as I have other patches in the

I think Matthew's idea gets us best of both worlds so I'd suggest to use it and resend the patch. You likely want to Cc stable@vger.kernel.org since the original patch this fixes got backported by Greg quite a bit since this was a rather long-standing issue. Please also Cc Andrew this time since he's likely going to pick it up.

Thanks for the patch! Christian

So you mean using page_address(ZERO_PAGE(0)) ? The idea is nice, but since struct ctl_table kern_table is declared as global variable, how can I assign it to the structure? GCC complains about 'initializer element is not constant', and ZERO_PAGE(0)->virtual only works if WANT_PAGE_VIRTUAL.

Anyway, I'm preparing a treewide patch to move all "zero", "one" and "int_max" to three single, const variables in fs/proc/proc_sysctl.c as there are 200+ occourrences of them, so I'd rather keep this simple to have it easily backported to stable.