Messages in this thread | | | Date | Mon, 22 Dec 2003 01:36:13 -0800 | From | Andrew Morton <> | Subject | Re: atomic copy_from_user? |
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Linus Torvalds <torvalds@osdl.org> wrote: > > > From some naughty place in the code where might_sleep > > would trigger, I'd like to read from user memory. > > I'll pretty much assume that mlockall() has been > > called. Suppose that "current" is correct as well. > > I'd just use a pointer directly, except that: > > > > a. it isn't OK for the 4g/4g feature, s390, or sparc64 > > b. it causes the "sparse" type checker to complain > > c. it will oops or worse if the user screwed up > > > > If the page is swapped out, I want a failed copy. > > the sequence > > local_bh_disable(); > err = get_user(n, ptr); > local_bh_enable(); > if (!err) > .. 'n' .. was the value > > will do this in 2.6.x, except it will complain loudly about the unatomic > access. Other than that, it will do what you ask for.
An explicit inc_preempt_count() would be clearer. See how ia32's kmap_atomic() does it. And filemap_copy_from_user().
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