Hi On Mon, 6 Jan 2014, Joonsoo Kim wrote: > Hello, > > I'm surprised that this VM_BUG_ON() has not been triggered until now. It was > introduced in 2007 by commit (b5fab14). Maybe there is no person who test > with CONFIG_DEBUG_VM. Last time I tried it, PS-RISC didn't work with CONFIG_DEBUG_VM at all. > There is one more bug report same as this. > * possible regression on 3.13 when calling flush_dcache_page > (lkml.org/lkml/2013/12/12/255) That link doesn't show anything. > As mentioned in the description of commit (b5fab14), slab object may not be > properly aligned and use of page oriented function to this object can be > dangerous. I searched the XFS code and found that they only try to allocate > multiple of 512 bytes, so there is no problem for now. But, IMHO, it is better > not to use slab objects for this purpose. If slab debugging is enabled, kmalloc memory is not aligned. In XFS in xfs_buf_allocate_memory they test if the kmalloc memory crosses page boundary - if it does, they free the kmalloc memory and allocate a full page. Maybe this approach could still run into problems with some bus-master adapters that assume alignment in hardware... dm-bufio also does I/O to slab-allocated buffers, but it allocates the object from slab (not kmalloc) with proper alignment. > And I rapidly searched every callsites of page_mapping() and, IMHO, this > patch would work correctly. But possibly reverting original commit is > better solution. Reverting the original commit wouldn't fix that VM_BUG_ON. > Hello, Pekka and Christoph. > Could you teach me which direction we have to go? > > Thanks. Mikulas -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
