On Thu, Jan 28, 2016 at 01:38:58PM -0800, Christoph Hellwig wrote: > On Thu, Jan 28, 2016 at 12:35:04PM -0700, Ross Zwisler wrote: > > There are a number of places in dax.c that look up the struct block_device > > associated with an inode. Previously this was done by just using > > inode->i_sb->s_bdev. This is correct for inodes that exist within the > > filesystems supported by DAX (ext2, ext4 & XFS), but when running DAX > > against raw block devices this value is NULL. This causes NULL pointer > > dereferences when these block_device pointers are used. > > It's also wrong for an XFS file system with a RT device.. > > > +#define DAX_BDEV(inode) (S_ISBLK(inode->i_mode) ? I_BDEV(inode) \ > > + : inode->i_sb->s_bdev) > > .. but this isn't going to fix it. You must use a bdev returned by > get_blocks or a similar file system method.
I guess I need to go off and understand if we can have DAX mappings on such a device. If we can, we may have a problem - we can get the block_device from get_block() in I/O path and the various fault paths, but we don't have access to get_block() when flushing via dax_writeback_mapping_range(). We avoid needing it the normal case by storing the sector results from get_block() in the radix tree. /me is off to play with RT devices...
