[lkml]   [2001]   [Oct]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Security question: "Text file busy" overwriting executables but not shared libraries?
In article <>,
Linus Torvalds <> wrote:
>The explicit flag is probably a good idea also because of usage patterns
>(PAGE_COPY is a slowdown _if_ the file is actually written to or even
>mapped shared).

Actually, I missed the obvious case: quite often when you do a "read()",
the reader itself will end up writing to the area read into. In which
case doing the PAGE_COPY would also slow down measurably, due to the
extra overhead of the copy-on-write fault (which not just does the copy
that we tried to avoid, but will take a fault and more VM locks).

So if we want to do this optimization, we _definitely_ want it to be
explicitly controlled by a flag, like O_DIRECT is. There are just too
many cases where it's a pessimization, and while the user can often tell
before-hand, the kernel simply cannot.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 13:08    [W:0.125 / U:0.176 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site