Compatible vdso's size is bigger than reserved buf

[Martin Welgemoed]

Hello everyone,

CRaC has been working quite well for us. Recently we upgraded
Kubernetes in GKE to 1.31 (kernel 6.6.72+) and since then CRaC
snapshots fail to restore with "Error: Compatible vdso's size is
bigger than reserved buf".

This is specifically for the 32bit compat VDSO. Running strace
confirms that the kernel now has it at 3 pages (12kb) in size.

arch_prctl(ARCH_MAP_VDSO_32, 0x7ffd1d983000) = 12288

In COMPAT_VDSO_BUF_SZ CRaC only allocates 2 pages for it
https://github.com/CRaC/criu/blob/e7aefe4f9e499597ddf484394d29fc4752b674dd/criu/vdso.c#L482

I'm somewhat surprised by it being 3 pages, because on my own local
machine (6.14.5-arch1-1) it is still 8kb:

arch_prctl(ARCH_MAP_VDSO_32, 0x789ea0a00000) = 8192

I think this is possibly a GKE configuration thing for its kernel build.

Does anyone else have experience with this or a solution for it? I
think increasing the COMPAT_VDSO_BUF_SZ could solve it but I am not
experienced enough with CRIU or the VDSO to fully judge the
implications of this.

Kind regards,

-- 
Martin Welgemoed
Scala Engineer

martin.welgemoed at commercetools.com
T. +49 (89) 99 82 996-0
commercetools B.V. | Prins Bernhardplein 200 | 1097 JB Amsterdam

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Prins Bernhardplein 200, 1097 JB Amsterdam | 
Netherlands
www.commercetools.com <http://www.commercetools.com/>


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