Re: hugemmap43: Migrate truncate_sigbus_versus_oom from libhugetlbfs

Hi Samir,

On Thu, Aug 20, 2026, Samir Mulani wrote:
> hugemmap43: Migrate truncate_sigbus_versus_oom from libhugetlbfs

> 	/* SIGBUS is what *should* happen */
> 	SAFE_FTRUNCATE(fdx, 0);
> 	if (sigsetjmp(sig_escape, 1) == 0)
> 		*((volatile unsigned int *)p);

Why is fdx truncated before faulting p? The original test keeps q
instantiated so that the hugepage pool remains exhausted. On a kernel
without ebed4bfc8da8, exhausting the pool makes allocation fail before the
missing i_size check, causing SIGKILL instead of SIGBUS.

Could this truncate be removed or moved after the fault? As written, it
releases the pages and no longer exercises the SIGBUS-versus-OOM regression
described by the commit message and test documentation.

> /*\
>  * Some kernels have a bug in the positioning of the test against
>  * i_size. This bug means that attempting to instantiate a page
>  * beyond the end of a hugepage file can result in an OOM and SIGKILL
>  * instead of the correct SIGBUS.
>  */
> [...]
> 	.needs_root = 1,

Could the description explain why root is required? LTP requires tests with
.needs_root to document the reason for the privilege requirement.

> +/hugetlb/hugemmap/hugemmap43

Could the binary instead be added to a .gitignore in the hugemmap directory?
LTP requires new test binaries to be ignored in their leaf test directory.

> 	SAFE_CLOSE(fd);
> 	SAFE_CLOSE(fdx);
> 	fd = -1;
> 	fdx = -1;

Could the explicit assignments be removed? SAFE_CLOSE() already sets each
descriptor argument to -1, and LTP's C test rules prohibit resetting it
manually.

Verdict - Needs revision

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