On Tue, 31 Mar 2009, Christoph Hellwig wrote: > On Mon, Mar 30, 2009 at 03:20:24PM -0400, Mikulas Patocka wrote: > > Hi > > > > I'm submitting this patch for 2.6.30 merge window. > > Please not. i_alloc_sem is really a horrible hack needed for a couple > filesystems only and we should not leak it into more generic code but > rather move the few instances into the filesystem. Could you please document locking rules for get_block(), truncate, bmap & direct i/o in Documentation/filesystems/Locking ? There is a lot of text about directories, but nothing about locking of block mappings. I was living under an impression that get_block() cannot be called on a block that is being truncated. That's what read/write/direct-io vs truncate seems to guarante --- truncate will first lower i_size (preventing any new pages past i_size from being created), then destroy any existing pages past i_size (that includes waiting for pagelock until all get_blocks on that page end) and finally truncate the metadata on the filesystem. So there should be no situation when you truncate block and call get_block on it simultaneously. If get_block can race with truncate, document it. There are filesystems that don't do any locking on get_block() (for example UFS, HPFS; FAT does it only for bmap and doesn't do it for general accesses) and other filesystems verify indirect block chains obsessively if they were truncated under get_block (why? because of bmap? or some other possibility?) --- so the rules should really be documented. Mikulas -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
