On Mon, 2 Jul 2007 19:19:26 +0200 Hoang-Nam Nguyen <[EMAIL PROTECTED]> wrote:
> For ehca device driver we're intending to utilize > idr_get_new_above() and have written a test case, which I'm attaching > at the end. Basically it tries to get an idr token above a lower boundary > by calling idr_get_new_above() and then uses idr_find() to check if > the returned token can be found. > Here is our observation with 2.6.22-rc7 on ppc64: > > Use lower boundary 0x3ffffffc > [EMAIL PROTECTED] idr_bug]# insmod idr_test_mod.ko start=1073741820 > insmod: error inserting 'idr_test_mod.ko': -1 Unknown symbol in module > [EMAIL PROTECTED] idr_bug]# dmesg -c > i=3ffffffc token=3ffffffc t=000000003ffffffc > i=3ffffffd token=3ffffffd t=000000003ffffffd > i=3ffffffe token=3ffffffe t=000000003ffffffe > i=3fffffff token=3fffffff t=000000003fffffff > i=40000000 token=40000000 t=0000000000000000 > Invalid object 0000000000000000. Expected 40000000 > > That means token 0x40000000 seems to be the "upper boundary" of idr_find(). > However the behaviour is not consistent in that it was returned by > idr_get_new_above(). > > Looking at void *idr_find(struct idr *idp, int id) > { > int n; > struct idr_layer *p; > > n = idp->layers * IDR_BITS; > p = idp->top; > > /* Mask off upper bits we don't use for the search. */ > id &= MAX_ID_MASK; > > if (id >= (1 << n)) > return NULL; > > while (n > 0 && p) { > n -= IDR_BITS; > p = p->ary[(id >> n) & IDR_MASK]; > } > return((void *)p); > } > we found that the if-condition has failed: > layers = 5 > IDR_BITS = 6 > n = 30 > (id >= (1 << n)) = (0x40000000 >= 0x40000000) = 1 > > Since MAX_ID_MASK=0x7fffffff, I'm wondering if 0x40000000 is the actual > upper boundary. Any hints or suggestions are appreciated. Looks like a bug to me. Really an IDR tree on 32-bit should go all the way up to 0xffffffff. Certainly up to 0x7fffffff. And the fact that idr_find() disagrees with idr_get_new_above() is a big hint that the code is getting it wrong. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/