Messages in this thread | | | Date | Sat, 24 Apr 1999 09:51:20 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: Q: generic_file_write sets PG_locked??? |
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On 24 Apr 1999, Eric W. Biederman wrote: > > Basically I contend that using PageLocked as a "data coherency lock" > is broken, at least when using the generic code.
It _isn't_ a data coherency lock at all: it's really a data structure coherency thing. Think of it as serialization protecting the internal data structures, and protecting the filesystem layer from ever getting confused about the order of reads and writes.
For example, a page cache entry always has to start out in a locked state, so that when a write occurs, we can fill in the page without any reader ever seeing the pre-write contents. If anybody was ever able to see those contents, we'd have serious security holes. That's why the write logic has to get the page lock early: not because of any real requirements for data coherency, but for a more subtle reason.
Linus
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