On 2025/10/8 15:09, Lance Yang wrote:
On 2025/10/8 14:14, Finn Thain wrote:
On Wed, 8 Oct 2025, Lance Yang wrote:
On 2025/10/8 08:40, Finn Thain wrote:
On Tue, 7 Oct 2025, Andrew Morton wrote:
Getting back to the $Subject at hand, are people OK with proceeding with Lance's original fix?
Lance's patch is probably more appropriate for -stable than the patch I proposed -- assuming a fix is needed for -stable.
Thanks!
Apart from that, I believe this fix is still needed for the hung task detector itself, to prevent unnecessary warnings in a few unexpected cases.
Can you be more specific about those cases? A fix for a theoretical bug doesn't qualify for -stable branches. But if it's a fix for a real bug, I have misunderstood Andrew's question...
I believe it is a real bug, as it was reported by Eero and Geert[1].
The blocker tracking mechanism in -stable assumes that lock pointers are at least 4-byte aligned. As I mentioned previously[2], this assumption fails for packed structs on architectures that don't trap on unaligned access.
Of course, we could always improve the mechanism to not make assumptions. But for -stable, this fix completely resolves the issue by ignoring any unaligned pointer, whatever the cause (e.g., packed structs, non-native alignment, etc.).
So we can all sleep well at night again :)
[1] https://lore.kernel.org/lkml/ CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc1_0g@mail.gmail.com/ [2] https://lore.kernel.org/lkml/cfb62b9d-9cbd-47dd- a894-3357027e2a50@linux.dev/
Forgot to add:
In other words, we are not just fixing the bug reported by Eero and Geert, but correcting the blocker tracking mechanism's flawed assumption for -stable ;)
If you feel this doesn't qualify as a fix, I can change the Fixes: tag to point to the original commit that introduced this flawed mechanism instead.
Besides those two alternatives, there is also a workaround: $ ./scripts/config -d DETECT_HUNG_TASK_BLOCKER which may be acceptable to the interested parties (i.e. m68k users).
I don't have a preference. I'll leave it up to the bug reporters (Eero and Geert).