Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965247AbWIEX6G (ORCPT ); Tue, 5 Sep 2006 19:58:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965233AbWIEX6E (ORCPT ); Tue, 5 Sep 2006 19:58:04 -0400 Received: from tetsuo.zabbo.net ([207.173.201.20]:693 "EHLO tetsuo.zabbo.net") by vger.kernel.org with ESMTP id S1422634AbWIEX56 (ORCPT ); Tue, 5 Sep 2006 19:57:58 -0400 From: Zach Brown To: linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, linux-kernel@vger.kernel.org Message-Id: <20060905235757.29630.86115.sendpatchset@tetsuo.zabbo.net> In-Reply-To: <20060905235732.29630.3950.sendpatchset@tetsuo.zabbo.net> References: <20060905235732.29630.3950.sendpatchset@tetsuo.zabbo.net> Subject: [RFC 5/5] dio: only call aio_complete() after returning -EIOCBQUEUED Date: Tue, 5 Sep 2006 16:57:57 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7051 Lines: 199 dio: only call aio_complete() after returning -EIOCBQUEUED The only time it is safe to call aio_complete() is when the ->ki_retry function returns -EIOCBQUEUED to the AIO core. direct_io_worker() has historically done this by relying on its caller to translate positive return codes into -EIOCBQUEUED for the aio case. It did this by trying to keep conditionals in sync. direct_io_worker() knew when finished_one_bio() was going to call aio_complete(). It would reverse the test and wait and free the dio in the cases it thought that finished_one_bio() wasn't going to. Not surprisingly, it ended up getting it wrong. 'ret' could be a negative errno from the submission path but it failed to communicate this to finished_one_bio(). direct_io_worker() would return < 0, it's callers wouldn't raise -EIOCBQUEUED, and aio_complete() would be called. In the future finished_one_bio()'s tests wouldn't reflect this and aio_complete() would be called for a second time which can manifest as an oops. The previous cleanups have whittled the sync and async completion paths down to the point where we can collapse them and clearly reassert the invariant that we must only call aio_complete() after returning -EIOCBQUEUED. direct_io_worker() will only return -EIOCBQUEUED when it is not the last to drop the dio refcount and the aio bio completion path will only call aio_complete() when it is the last to drop the dio refcount. direct_io_worker() can ensure that it is the last to drop the reference count by waiting for bios to drain. It does this for sync ops, of course, and for partial dio writes that must fall back to buffered and for aio ops that saw errors during submission. This means that operations that end up waiting, even if they were issued as aio ops, will not call aio_complete() from dio. Instead we return the return code of the operation and let the aio core call aio_complete(). This is purposely done to fix a bug where AIO DIO file extensions would call aio_complete() before their callers have a chance to update i_size. Now that direct_io_worker() is explicitly returning -EIOCBQUEUED its callers no longer have to translate for it. Signed-off-by: Zach Brown --- fs/direct-io.c | 92 ++++++++++++++++++----------------------------- mm/filemap.c | 4 -- 2 files changed, 36 insertions(+), 60 deletions(-) Index: 2.6.18-rc6-dio-cleanup/fs/direct-io.c =================================================================== --- 2.6.18-rc6-dio-cleanup.orig/fs/direct-io.c +++ 2.6.18-rc6-dio-cleanup/fs/direct-io.c @@ -225,6 +225,15 @@ static int dio_complete(struct dio *dio, { ssize_t transferred = 0; + /* + * AIO submission can race with bio completion to get here while + * expecting to have the last io completed by bio completion. + * In that case -EIOCBQUEUED is in fact not an error we want + * to preserve through this call. + */ + if (ret == -EIOCBQUEUED) + ret = 0; + if (dio->result) { transferred = dio->result; @@ -250,24 +259,6 @@ static int dio_complete(struct dio *dio, return ret; } -/* - * Called when a BIO has been processed. If the count goes to zero then IO is - * complete and we can signal this to the AIO layer. - */ -static void dio_complete_aio(struct dio *dio) -{ - int ret; - - ret = dio_complete(dio, dio->iocb->ki_pos, 0); - - /* Complete AIO later if falling back to buffered i/o */ - if (dio->result == dio->size || - ((dio->rw == READ) && dio->result)) { - aio_complete(dio->iocb, ret, 0); - kfree(dio); - } -} - static int dio_bio_complete(struct dio *dio, struct bio *bio); /* * Asynchronous IO callback. @@ -289,8 +280,11 @@ static int dio_bio_end_aio(struct bio *b if (remaining == 1 && waiter_holds_ref) wake_up_process(dio->waiter); - if (remaining == 0) - dio_complete_aio(dio); + if (remaining == 0) { + int ret = dio_complete(dio, dio->iocb->ki_pos, 0); + aio_complete(dio->iocb, ret, 0); + kfree(dio); + } return 0; } @@ -1074,47 +1068,33 @@ direct_io_worker(int rw, struct kiocb *i mutex_unlock(&dio->inode->i_mutex); /* - * OK, all BIOs are submitted, so we can decrement bio_count to truly - * reflect the number of to-be-processed BIOs. - */ - if (dio->is_async) { - int should_wait = 0; - - if (dio->result < dio->size && (rw & WRITE)) { - dio->waiter = current; - should_wait = 1; - } - if (ret == 0) - ret = dio->result; - - if (should_wait) - dio_await_completion(dio); - - /* this can free the dio */ - if (atomic_dec_and_test(&dio->refcount)) - dio_complete_aio(dio); + * The only time we want to leave bios in flight is when a successful + * partial aio read or full aio write have been setup. In that case + * bio completion will call aio_complete. The only time it's safe to + * call aio_complete is when we return -EIOCBQUEUED, so we key on that. + * This had *better* be the only place that raises -EIOCBQUEUED. + */ + BUG_ON(ret == -EIOCBQUEUED); + if (dio->is_async && ret == 0 && dio->result && + ((rw & READ) || (dio->result == dio->size))) + ret = -EIOCBQUEUED; - if (should_wait) - kfree(dio); - } else { + if (ret != -EIOCBQUEUED) dio_await_completion(dio); + /* + * Sync will always be dropping the final ref and completing the + * operation. AIO can if it was a broken operation described above + * or in fact if all the bios race to complete before we get here. + * In that case dio_complete() translates the EIOCBQUEUED into + * the proper return code that the caller will hand to aio_complete(). + */ + if (atomic_dec_and_test(&dio->refcount)) { ret = dio_complete(dio, offset, ret); + kfree(dio); + } else + BUG_ON(ret != -EIOCBQUEUED); - /* We could have also come here on an AIO file extend */ - if (!is_sync_kiocb(iocb) && (rw & WRITE) && - ret >= 0 && dio->result == dio->size) - /* - * For AIO writes where we have completed the - * i/o, we have to mark the the aio complete. - */ - aio_complete(iocb, ret, 0); - - if (atomic_dec_and_test(&dio->refcount)) - kfree(dio); - else - BUG(); - } return ret; } Index: 2.6.18-rc6-dio-cleanup/mm/filemap.c =================================================================== --- 2.6.18-rc6-dio-cleanup.orig/mm/filemap.c +++ 2.6.18-rc6-dio-cleanup/mm/filemap.c @@ -1175,8 +1175,6 @@ __generic_file_aio_read(struct kiocb *io if (pos < size) { retval = generic_file_direct_IO(READ, iocb, iov, pos, nr_segs); - if (retval > 0 && !is_sync_kiocb(iocb)) - retval = -EIOCBQUEUED; if (retval > 0) *ppos = pos + retval; } @@ -2053,8 +2051,6 @@ generic_file_direct_write(struct kiocb * if (err < 0) written = err; } - if (written == count && !is_sync_kiocb(iocb)) - written = -EIOCBQUEUED; return written; } EXPORT_SYMBOL(generic_file_direct_write); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/