Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Sat, 7 Mar 2015, Jens Axboe wrote: > >>> mempool_alloc() does not support __GFP_ZERO since elements may come from > >>> memory that has already been released by mempool_free(). > >>> > >>> Remove __GFP_ZERO from mempool_alloc() in drbd_req_new() and properly > >>> initialize it to 0. > >> > >> You should add it to mempool instead, avoid having this issue show up for > >> other folks as well. It'd be trivial to do. Normal ->alloc() should honor > >> __GFP_ZERO, just do the same manually for removing an item from the internal > >> pool. > >> > > > > Umm, it's not trivial to do and wouldn't make sense to do it. Mempools > > Uhm, it would make sense, though. > Disagree, I don't think we should extend mempool to know the element size, modify every user of mempool to pass it in, and keep it consistent with mempool_alloc_t for the benefit of __GFP_ZERO for this one buggy caller. Most users don't need __GFP_ZERO and just overwrite the entire element after mempool_alloc() and it would be an unnecessary overhead to even check for the bit set. So it wouldn't make sense in terms of performance or maintainability. > > don't know the element size, in other words it wouldn't know the length to > > memset() to 0 for mempool_alloc(). It shouldn't be modified to know the > > element size since elements are allocated by the implementation of > > mempool_alloc_t and they could easily become inconsistent. This patch is > > what you want to merge, really. > > > > I forgot we don't have the size in there. Then I would suggest adding a > WARN_ON() for __GFP_ZERO being set in mempool_alloc(), at the very least. > There is, it's a VM_WARN_ON_ONCE() that will show up if you configure CONFIG_DEBUG_VM.