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[174.109.172.136]) by smtp.gmail.com with ESMTPSA id z7sm2725764qtc.10.2020.09.22.07.17.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Sep 2020 07:17:59 -0700 (PDT) Subject: Re: [PATCH 03/15] iomap: Allow filesystem to call iomap_dio_complete without i_rwsem To: Goldwyn Rodrigues , linux-fsdevel@vger.kernel.org Cc: linux-btrfs@vger.kernel.org, david@fromorbit.com, hch@lst.de, johannes.thumshirn@wdc.com, dsterba@suse.com, darrick.wong@oracle.com, Goldwyn Rodrigues References: <20200921144353.31319-1-rgoldwyn@suse.de> <20200921144353.31319-4-rgoldwyn@suse.de> From: Josef Bacik Message-ID: <9c669220-a5d9-48fe-8e0e-e2c3d3de5695@toxicpanda.com> Date: Tue, 22 Sep 2020 10:17:58 -0400 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.2.2 MIME-Version: 1.0 In-Reply-To: <20200921144353.31319-4-rgoldwyn@suse.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 9/21/20 10:43 AM, Goldwyn Rodrigues wrote: > From: Christoph Hellwig > > This is to avoid the deadlock caused in btrfs because of O_DIRECT | > O_DSYNC. > > Filesystems such as btrfs require i_rwsem while performing sync on a > file. iomap_dio_rw() is called under i_rw_sem. This leads to a > deadlock because of: > > iomap_dio_complete() > generic_write_sync() > btrfs_sync_file() > > Separate out iomap_dio_complete() from iomap_dio_rw(), so filesystems > can call iomap_dio_complete() after unlocking i_rwsem. > > Signed-off-by: Goldwyn Rodrigues > --- > fs/iomap/direct-io.c | 34 +++++++++++++++++++++++++--------- > include/linux/iomap.h | 5 +++++ > 2 files changed, 30 insertions(+), 9 deletions(-) > > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c > index c1aafb2ab990..d970c6bbbe11 100644 > --- a/fs/iomap/direct-io.c > +++ b/fs/iomap/direct-io.c > @@ -76,7 +76,7 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap, > dio->submit.cookie = submit_bio(bio); > } > > -static ssize_t iomap_dio_complete(struct iomap_dio *dio) > +ssize_t iomap_dio_complete(struct iomap_dio *dio) > { > const struct iomap_dio_ops *dops = dio->dops; > struct kiocb *iocb = dio->iocb; > @@ -130,6 +130,7 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio) > > return ret; > } > +EXPORT_SYMBOL_GPL(iomap_dio_complete); > > static void iomap_dio_complete_work(struct work_struct *work) > { > @@ -406,8 +407,8 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length, > * Returns -ENOTBLK In case of a page invalidation invalidation failure for > * writes. The callers needs to fall back to buffered I/O in this case. > */ > -ssize_t > -iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, > +struct iomap_dio * > +__iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, > const struct iomap_ops *ops, const struct iomap_dio_ops *dops, > bool wait_for_completion) > { > @@ -421,14 +422,14 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, > struct iomap_dio *dio; > > if (!count) > - return 0; > + return NULL; > > if (WARN_ON(is_sync_kiocb(iocb) && !wait_for_completion)) > - return -EIO; > + return ERR_PTR(-EIO); > > dio = kmalloc(sizeof(*dio), GFP_KERNEL); > if (!dio) > - return -ENOMEM; > + return ERR_PTR(-ENOMEM); > > dio->iocb = iocb; > atomic_set(&dio->ref, 1); > @@ -558,7 +559,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, > dio->wait_for_completion = wait_for_completion; > if (!atomic_dec_and_test(&dio->ref)) { > if (!wait_for_completion) > - return -EIOCBQUEUED; > + return ERR_PTR(-EIOCBQUEUED); > > for (;;) { > set_current_state(TASK_UNINTERRUPTIBLE); > @@ -574,10 +575,25 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, > __set_current_state(TASK_RUNNING); > } > > - return iomap_dio_complete(dio); > + return dio; > > out_free_dio: > kfree(dio); > - return ret; > + return ERR_PTR(ret); > +} > +EXPORT_SYMBOL_GPL(__iomap_dio_rw); > + > +ssize_t > +iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, > + const struct iomap_ops *ops, const struct iomap_dio_ops *dops, > + bool wait_for_completion) > +{ > + struct iomap_dio *dio; > + > + dio = __iomap_dio_rw(iocb, iter, ops, dops, wait_for_completion); > + if (IS_ERR_OR_NULL(dio)) > + return PTR_ERR_OR_ZERO(dio); > + return iomap_dio_complete(dio); > } > EXPORT_SYMBOL_GPL(iomap_dio_rw); > + Got an extra + here for some reason. Otherwise Reviewed-by: Josef Bacik Thanks, Josef