On Fri, 2006-09-01 at 17:12 +0100, Anton Altaparmakov wrote: > Hi, > > On Fri, 1 Sep 2006, Badari Pulavarty wrote: > > > > I have been running into following bug while running fsx > > tests on 1k (ext3) filesystem all the time. > > > > ----------- [cut here ] --------- [please bite here ] --------- > > Kernel BUG at fs/buffer.c:2791 > > invalid opcode: 0000 [1] SMP > > > > Its complaining about BUG_ON(!buffer_mapped(bh)). > > > > It was hard to track it down, needed lots of debug - but here > > is the problem & fix. Since the fix is in __set_page_buffer_dirty() > > code - I am wondering how it would effect others :( > > This will breaks NTFS and probably a lot of other file systems I would > think. Well, it can happen only with fileystems with blocksize < pagesize. So, that should limit the scope :) > > For example all buffer based file systems in their writepage > implementations will create buffers if none are present and those will not > be mapped. If for whatever reason writepage now breaks out before mapping > the buffers (e.g. because the buffers do not need to be written or due to > an error) you are left with a page containing unmapped buffers. > > Then a page dirty comes in caused by a mmapped write for example. > > __set_page_dirty_bufferes() runs by default and with your patch does not > set the unmapped buffers dirty thus they never get written out and you > have data corruption. I was wondering, is it *okay* to have a dirty buffer but not mapped to disk ? I guess, so .. > > It is the caller of submit_bh() that is doing the stupidity of submitting > unmapped buffers for i/o or even the caller of the caller, etc... > Somewhere up in that chain buffers should have been mapped before being > submitted for i/o otherwise it is a BUG() (as correctly identified by > submit_bh()). > > Perhaps the real fix is not to have ext3 use ll_rw_block() and instead > make it use submit_bh() directly and only submit buffers inside the file > size and/or make it map buffers before calling ll_rw_block() and if they > are outside the file size just clean them without submitting them... Yeah. I considered doing it in ll_rw_block() - but then I thought fixing it in set_page_buffer_dirty() may be a valid fix :( Let me try other options, then. Thanks, Badari - 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
