On Thu, Dec 03, 2015 at 08:41:29PM +0800, Herbert Xu wrote: > On Mon, Nov 30, 2015 at 06:18:59PM +0800, Herbert Xu wrote: > > > > OK that's better. I think I see the problem. The test in > > rhashtable_insert_rehash is racy and if two threads both try > > to grow the table one of them may be tricked into doing a rehash > > instead. > > > > I'm working on a fix. > > OK this patch fixes the EBUSY problem as far as I can tell. Please > let me know if you still observe EBUSY with it. I'll respond to the > ENOMEM problem in another email. > > ---8<--- > Thomas and Phil observed that under stress rhashtable insertion > sometimes failed with EBUSY, even though this error should only > ever been seen when we're under attack and our hash chain length > has grown to an unacceptable level, even after a rehash. > > It turns out that the logic for detecting whether there is an > existing rehash is faulty. In particular, when two threads both > try to grow the same table at the same time, one of them may see > the newly grown table and thus erroneously conclude that it had > been rehashed. This is what leads to the EBUSY error. > > This patch fixes this by remembering the current last table we > used during insertion so that rhashtable_insert_rehash can detect > when another thread has also done a resize/rehash. When this is > detected we will give up our resize/rehash and simply retry the > insertion with the new table. > > Reported-by: Thomas Graf <tg...@suug.ch> > Reported-by: Phil Sutter <p...@nwl.cc> > Signed-off-by: Herbert Xu <herb...@gondor.apana.org.au>
Tested-by: Phil Sutter <p...@nwl.cc> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
