Re: [PATCH v2] nvdimm/pmem: Release gendisk on probe failure

[Hemanth Selam]

On Mon, Aug 31, 2026 at 04:45:08AM +0000, sashiko-bot@xxxxxxxxxx wrote:
> This isn't a bug introduced by this patch, but I wanted to ask about the error
> handling for alloc_dax() just below this code.
>
> In pmem_attach_disk(), if alloc_dax() fails with -EOPNOTSUPP, the code
> gracefully falls back and leaves pmem->dax_dev as NULL:
[...]
> However, the write_cache sysfs attribute remains unconditionally visible as long
> as CONFIG_ARCH_HAS_PMEM_API is enabled.

I do not think the two can meet.  alloc_dax() only returns -EOPNOTSUPP for

	if (ops && cpu_dcache_is_aliasing())
		return ERR_PTR(-EOPNOTSUPP);

so pmem->dax_dev is left NULL only on architectures whose data caches are
virtually aliased: csky, m68k, parisc and sh unconditionally, arm and mips
depending on the CPU.

write_cache is visible only when CONFIG_ARCH_HAS_PMEM_API is selected, and
that is arm64, powerpc, riscv and x86_64 (X86_64 only), none of which have
aliasing data caches.  So on every architecture where alloc_dax() can hand
back -EOPNOTSUPP, dax_visible() returns 0 for write_cache and there is
nothing to read.

Happy to be shown otherwise if there is a configuration I am missing, in
which case the fix belongs in dax_visible() rather than in this patch.

Hemanth