On 13.01.21 22:53, Dave Chinner wrote:
[...]
I agree that a throttling fix is needed, but I'm trying to
understand the scope and breadth of the problem first instead of
jumping the gun and making the wrong fix for the wrong reasons that
just papers over the underlying problems that the throttling bug has
made us aware of...
Are you still working on this?
If it takes more time to understand the potential underlying problem, the fix for the problem at hand should be applied.
This is a real world problem, accidentally found in the wild. It appears very rarely, but it freezes a filesystem or the whole system. It exists in 5.7 , 5.8 , 5.9 , 5.10 and 5.11 and is caused by c7f87f3984cf ("xfs: fix use-after-free on CIL context on shutdown") which silently added a condition to the wakeup. The condition is based on a wrong assumption.
Why is this "papering over"? If a reminder was needed, there were better ways than randomly hanging the system.
Why is
if (ctx->space_used >= XLOG_CIL_BLOCKING_SPACE_LIMIT(log))
wake_up_all(&cil->xc_push_wait);
, which doesn't work reliably, preferable to
if (waitqueue_active(&cil->xc_push_wait))
wake_up_all(&cil->xc_push_wait);
which does?
Best
Donald
Cheers,
Dave
