Messages in this thread |  | | From | Paul Mackerras <> | Date | Tue, 4 Sep 2001 11:53:22 +1000 (EST) | Subject | Re: [PATCH] avoid unnecessary cache flushes |
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Richard Henderson writes:
> You can get a missed flush from > > bit == 0 > flush cache > > modify page > bit = 0 > > bit = 1 > > unless this is protected from some outer lock of which > I am not aware.
The page is question is one which is mapped (is being mapped) into a process's address space with execute permission. If the page is part of the page cache for a file, then I would have thought that attempts to write to the page would return an ETXTBSY error. If the page is a private page (private COW or anonymous page) then I don't see where the kernel would be modifying the page. If it is already mapped into another process's address space with a shared writable mapping, and that process is writing to the page, then it is up to the user-level stuff to do the necessary cache-flushing.
So I think it's OK at the moment, but I agree it does look like a race waiting to happen.
For alpha, the thing that my patch does that might hurt is the change from flush_icache_page to flush_icache_range in kernel/ptrace.c. Any comment on that?
Paul.
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