Re: Assumed Failure rates in Various o.s's ?

[Erik Corry <erik@arbat.com>]

On Fri, May 21, 1999 at 10:25:42AM -0400, Benjamin C.R. LaHaise wrote:
> On Fri, 21 May 1999, Erik Corry wrote:
> 
> > According to Andi you already fixed this with a read lock that
> > prevents mmap and mmunmap from doing anything while the copy
> > is running.  This makes sense, since if you do it right with a
> > readers/writers lock you can keep out mmap without serialising
> > copy_to_user or copy_from_user.
> 
> I really like the cleanliness of this approach, but it's troublesome:
> memory allocations in other threads would then get blocked during large
> IOs -- very bad.

Actually, isn't it just munmap that is problematic?

After the access_ok you can't map a read-only file into the
path of an oncoming copy_to_user without first unmapping
what was there before (this is assuming a version of
access_ok that checks whether something was mapped).
So mmaps can safely happen in parallel with copy_to_user.

-- 
Erik Corry erik@arbat.com           Ceterum censeo, Microsoftem esse delendam!
--
To unsubscribe, send a message with 'unsubscribe linux-mm my@address'
in the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://humbolt.geo.uu.nl/Linux-MM/