Re: [PATCH] atomic: Specify natural alignment for atomic_t

[Eero Tamminen]

Hi Finn & Lance,

On 25.8.2025 5.03, Finn Thain wrote:
> Some recent commits incorrectly assumed the natural alignment of locks.
> That assumption fails on Linux/m68k (and, interestingly, would have failed
> on Linux/cris also). This leads to spurious warnings from the hang check
> code. Fix this bug by adding the necessary 'aligned' attribute.
[...]
> Reported-by: Eero Tamminen <oak@xxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc1_0g@xxxxxxxxxxxxxx/
> Fixes: e711faaafbe5 ("hung_task: replace blocker_mutex with encoded blocker")
> Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxx>
> ---
> I tested this on m68k using GCC and it fixed the problem for me. AFAIK,
> the other architectures naturally align ints already so I'm expecting to
> see no effect there.

Yes, it fixes both of the issues (warnings & broken console):
	Tested-by: Eero Tamminen <oak@xxxxxxxxxxxxxx>

(Emulated Atari Falcon) boot up performance with this is within normal 
variation.


On 23.8.2025 10.49, Lance Yang wrote:
> Anyway, I've prepared two patches for discussion, either of which should
> fix the alignment issue :)
>
> Patch A[1] adjusts the runtime checks to handle unaligned pointers.
> Patch B[2] enforces 4-byte alignment on the core lock structures.
>
> Both tested on x86-64.
>
> [1] 
https://lore.kernel.org/lkml/20250823050036.7748-1-lance.yang@xxxxxxxxx
> [2] https://lore.kernel.org/lkml/20250823074048.92498-1-
> lance.yang@xxxxxxxxx

Same goes for both of these, except that removing warnings makes minimal 
kernel boot 1-2% faster than 4-aligning the whole struct.


	- Eero