From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Date: Wed, 21 Mar 2018 07:23:40 +0000 Subject: Re: [PATCH] [RFC] target/file: add support of direct and async I/O Message-Id: <20180321072340.GA29587@infradead.org> List-Id: References: <20180309004259.16052-1-avagin@openvz.org> In-Reply-To: <20180309004259.16052-1-avagin@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: target-devel@vger.kernel.org > I'm afraid this patch doesn't work, because we are not always allocate bvec, > sometimes we get it from bio. In this case, we have to call > blk_mq_complete_request after read_iter/write_iter. The issue there is that we really need to NULL ->bvec after freeing it. Which normally is an anti-pattern but seems to be needed here (and warrants a comment). Updated patch below: >From b8eed7302071023852c00f8296165c2e9bbc51f4 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Tue, 20 Mar 2018 09:35:55 +0100 Subject: loop: remove loop_cmd refcounting Instead of introducing an unneeded refcount free the bvec after calling into ->read_iter and ->write_iter, which follows the the normal read/write path conventions. Fixes: 92d77332 ("block/loop: fix use after free") Signed-off-by: Christoph Hellwig --- drivers/block/loop.c | 19 +++++++------------ drivers/block/loop.h | 1 - 2 files changed, 7 insertions(+), 13 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index ee62d2d517bf..9cb6078cd4f0 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -463,15 +463,6 @@ static void lo_complete_rq(struct request *rq) blk_mq_end_request(rq, cmd->ret < 0 ? BLK_STS_IOERR : BLK_STS_OK); } -static void lo_rw_aio_do_completion(struct loop_cmd *cmd) -{ - if (!atomic_dec_and_test(&cmd->ref)) - return; - kfree(cmd->bvec); - cmd->bvec = NULL; - blk_mq_complete_request(cmd->rq); -} - static void lo_rw_aio_complete(struct kiocb *iocb, long ret, long ret2) { struct loop_cmd *cmd = container_of(iocb, struct loop_cmd, iocb); @@ -479,7 +470,7 @@ static void lo_rw_aio_complete(struct kiocb *iocb, long ret, long ret2) if (cmd->css) css_put(cmd->css); cmd->ret = ret; - lo_rw_aio_do_completion(cmd); + blk_mq_complete_request(cmd->rq); } static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, @@ -527,7 +518,6 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter); segments = bio_segments(bio); } - atomic_set(&cmd->ref, 2); iov_iter_bvec(&iter, ITER_BVEC | rw, bvec, segments, blk_rq_bytes(rq)); @@ -545,7 +535,12 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, else ret = call_read_iter(file, &cmd->iocb, &iter); - lo_rw_aio_do_completion(cmd); + /* + * Clear bvec to NULL as lo_rw_aio only allocates and sets it for + * the multiple bios per request case and we want a clean slate here. + */ + kfree(cmd->bvec); + cmd->bvec = NULL; kthread_associate_blkcg(NULL); if (ret != -EIOCBQUEUED) diff --git a/drivers/block/loop.h b/drivers/block/loop.h index 0f45416e4fcf..ba65848c7c33 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -68,7 +68,6 @@ struct loop_cmd { struct kthread_work work; struct request *rq; bool use_aio; /* use AIO interface to handle I/O */ - atomic_t ref; /* only for aio */ long ret; struct kiocb iocb; struct bio_vec *bvec; -- 2.14.2