Messages in this thread | | | Date | Mon, 06 Nov 2017 16:15:29 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v17 1/6] lib/xbitmap: Introduce xbitmap |
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On 11/03/2017 06:55 PM, Tetsuo Handa wrote: > I'm commenting without understanding the logic. > > Wei Wang wrote: >> + >> +bool xb_preload(gfp_t gfp); >> + > Want __must_check annotation, for __radix_tree_preload() is marked > with __must_check annotation. By error failing to check result of > xb_preload() will lead to preemption kept disabled unexpectedly. >
I don't disagree with this, but I find its wrappers, e.g. radix_tree_preload() and radix_tree_maybe_preload(), don't seem to have __must_chek added.
> >> +int xb_set_bit(struct xb *xb, unsigned long bit) >> +{ >> + int err; >> + unsigned long index = bit / IDA_BITMAP_BITS; >> + struct radix_tree_root *root = &xb->xbrt; >> + struct radix_tree_node *node; >> + void **slot; >> + struct ida_bitmap *bitmap; >> + unsigned long ebit; >> + >> + bit %= IDA_BITMAP_BITS; >> + ebit = bit + 2; >> + >> + err = __radix_tree_create(root, index, 0, &node, &slot); >> + if (err) >> + return err; >> + bitmap = rcu_dereference_raw(*slot); >> + if (radix_tree_exception(bitmap)) { >> + unsigned long tmp = (unsigned long)bitmap; >> + >> + if (ebit < BITS_PER_LONG) { >> + tmp |= 1UL << ebit; >> + rcu_assign_pointer(*slot, (void *)tmp); >> + return 0; >> + } >> + bitmap = this_cpu_xchg(ida_bitmap, NULL); >> + if (!bitmap) > Please write locking rules, in order to explain how memory > allocated by __radix_tree_create() will not leak. >
For the memory allocated by __radix_tree_create(), I think we could add:
if (!bitmap) { __radix_tree_delete(root, node, slot); break; }
For the locking rules, how about adding the following "Developer notes:" at the top of the file:
" Locks are required to ensure that concurrent calls to xb_set_bit, xb_preload_and_set_bit, xb_test_bit, xb_clear_bit, xb_clear_bit_range, xb_find_next_set_bit and xb_find_next_zero_bit, for the same ida bitmap will not happen. "
>> +bool xb_test_bit(struct xb *xb, unsigned long bit) >> +{ >> + unsigned long index = bit / IDA_BITMAP_BITS; >> + const struct radix_tree_root *root = &xb->xbrt; >> + struct ida_bitmap *bitmap = radix_tree_lookup(root, index); >> + >> + bit %= IDA_BITMAP_BITS; >> + >> + if (!bitmap) >> + return false; >> + if (radix_tree_exception(bitmap)) { >> + bit += RADIX_TREE_EXCEPTIONAL_SHIFT; >> + if (bit > BITS_PER_LONG) > Why not bit >= BITS_PER_LONG here?
Yes, I think it should be ">=" here. Thanks.
Best, Wei
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