[Bug 220272] Latent race condition in USB code unveiled with optimized memset_64.S

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=220272

--- Comment #28 from Oliver Neukum (oliver@neukum.org) ---
(In reply to Alan Stern from comment #27)
> But if that's the explanation then why does the driver work properly some of
> the time?

Memory pressure on the cache. Sometimes cache lines will be invalidated.
If you want to stay with the theory that this is a cache issue.

Your diagnosis in #23 is correct. The driver is operating on a zeroed buffer.
If we are also taking #25 then we'd have to assume that two different mice fail
in the same way, but inconsistently and only if a specific memset is used.
Not really likely.

My first suspicion was that we are looking at an issue with HCD with short
transfers, specifically that te buffer is not really used and the IO done to
the rings, but I see no way how this would correlate with a change in memset.

Do we need to memset the buffers to 0x00? How about a diagnostic patch that
uses another value?

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