On Mon, Jul 26, 2010 at 12:23:10PM +0200, Andre Przywara wrote: > Andi Kleen wrote: > >On Mon, Jul 26, 2010 at 11:28:18AM +0200, Andre Przywara wrote: > >>When the mbind() syscall implementation processes the node mask > >>provided by the user, the last node is accidentally masked out. > >>This is present since the dawn of time (aka Before Git), I guess > >>nobody realized that because libnuma as the most prominent user of > >>mbind() uses large masks (sizeof(long)) and nobody cared if the > >>64th node is not handled properly. But if the user application > >>defers the masking to the kernel and provides the number of valid bits > >>in maxnodes, there is always the last node missing. > >>However this also affect the special case with maxnodes=0, the manpage > >>reads that mbind(ptr, len, MPOL_DEFAULT, &some_long, 0, 0); should > >>reset the policy to the default one, but in fact it returns EINVAL. > >>This patch just removes the decrease-by-one statement, I hope that > >>there is no workaround code in the wild that relies on the bogus > >>behavior. > > > >Actually libnuma and likely most existing users rely on it. > If grep didn't fool me, then the only users in libnuma aware of that > bug are the test implementations in numactl-2.0.3/test, namely > /test/tshm.c (NUMA_MAX_NODES+1) and test/mbind_mig_pages.c > (old_nodes->size + 1). At least libnuma 1 (which is the libnuma most distributions use today) explicitely knows about it and will break if you change it. > > Has this bug been known before? Yes (and you can argue whether it's a problem or not) -Andi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>