On 05/31/2012 10:08 PM, Jeff Moyer wrote: > Junxiao Bi <[email protected]> writes: > >> Ocfs2 uses kiocb.*private as a flag of unsigned long size. In >> commit a11f7e6 ocfs2: serialize unaligned aio, the unaligned >> io flag is involved in it to serialize the unaligned aio. As >> *private is not initialized in init_sync_kiocb() of do_sync_write(), >> this unaligned io flag may be unexpectly set in an aligned dio. >> And this will cause OCFS2_I(inode)->ip_unaligned_aio decreased >> to -1 in ocfs2_dio_end_io(), thus the following unaligned dio >> will hang forever at ocfs2_aiodio_wait() in ocfs2_file_write_iter(). >> We can't initialized this flag in ocfs2_file_write_iter() since >> it may be invoked several times by do_sync_write(). So we initialize >> it in init_sync_kiocb(), it's also useful for other similiar use of >> it in the future. > I don't see any ocfs2_file_write_iter in the upstream kernel. > ocfs2_file_aio_write most certainly could set ->private to 0, it > will only be called once for a given kiocb. >From sys_io_submit->..->io_submit_one->aio_run_iocb->aio_rw_vect_retry, it seems that aio_write could be called two times. See the following scenario. 1. There is a file opened with direct io flag, in aio_rw_vect_retry, aio_write is called first time. If the direct io can not be completed, it will fall back into buffer io, see line 2329 in aio_write. 2. If the very buffer io is a partial write, then it will return back to aio_rw_vect_retry and issue the second aio_write. > > That point aside, I have no issues with setting private to NULL in > init_sync_kiocb. If you fix up the comment to reflect reality > w.r.t. the upstream kernel source, I'll ack the patch. OK, I will fix the comment. > > Cheers, > Jeff
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