Messages in this thread | | | Date | Fri, 15 Oct 1999 20:26:25 +0200 | From | Manfred Spraul <> | Subject | Re: [PATCH] kanoj-mm17-2.3.21 kswapd vma scanning protection |
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Kanoj Sarcar wrote: > If you wanted to be more careful, you > could define the swapout prototype as swapout(start, end, flags, file). > That *should* be enough for most future 2.3/2.4 driver.
"file" can go away if you do not call "get_file()" before releasing the locking.
> > > - swap_out() is called with the semaphore held, > > Look below for why this is not safe. You are right, this can lock-up. Swapper is only protected from reentrancy on it's own stack, not from reentrancy from another thread.
> > > Or: ->swapout() releases the semaphore, > > > > This works for filemap_swapout, but you can not expect every regular Joe > driver writer to adhere to this rule. The result is not a rare lock-up, but it will lock-up nearly immediately. Even Joe would notice that. [I know this is ugly]
> And here's one more. Before invoking swapout(), and before loosing the > vmlist_lock in try_to_swap_out, the vma might be marked with a flag > that indicates that swapout() is looking at the vma. Or: use a multiple reader - single writer semaphore with "starve writer" policy. IMO that's cleaner than a semaphore with an attached waitqueue for do_munmap().
> This swapout() cleanup is independent of the patch I have already posted, > so the patch should be integrated into 2.3, while we debate how to tackle > the cleanup.
Ok.
-- Manfred
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