From: Eric Sandeen Subject: Re: [PATCH v2 1/2] ext4: Close race between direct IO and ext4_break_layouts() Date: Mon, 10 Sep 2018 11:23:56 -0500 Message-ID: References: <153374910694.40645.17166196534680658204.stgit@djiang5-desk3.ch.intel.com> Reply-To: sandeen-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org, david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org, linux-xfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, lczerner-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, hch-jcswGhMUV9g@public.gmane.org To: Dave Jiang , tytso-3s7WtUTddSA@public.gmane.org, darrick.wong-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, jack-AlSwsSmVLrQ@public.gmane.org, zwisler-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org Return-path: In-Reply-To: <153374910694.40645.17166196534680658204.stgit-Cxk7aZI4ujnJARH06PadV2t3HXsI98Cx0E9HWUfgJXw@public.gmane.org> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" List-Id: linux-ext4.vger.kernel.org On 8/8/18 12:25 PM, Dave Jiang wrote: > From: Ross Zwisler > > If the refcount of a page is lowered between the time that it is returned > by dax_busy_page() and when the refcount is again checked in > ext4_break_layouts() => ___wait_var_event(), the waiting function > ext4_wait_dax_page() will never be called. This means that > ext4_break_layouts() will still have 'retry' set to false, so we'll stop > looping and never check the refcount of other pages in this inode. > > Instead, always continue looping as long as dax_layout_busy_page() gives us > a page which it found with an elevated refcount. > > Signed-off-by: Ross Zwisler > Reviewed-by: Jan Kara Ted - wondering if this one is still on your radar? Thanks, -Eric > --- > > v2: > - remove verbiage in comment header (Jan) > > fs/ext4/inode.c | 9 +++------ > 1 file changed, 3 insertions(+), 6 deletions(-) > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index 8f6ad7667974..d2663a1e3ec2 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -4191,9 +4191,8 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset, > return 0; > } > > -static void ext4_wait_dax_page(struct ext4_inode_info *ei, bool *did_unlock) > +static void ext4_wait_dax_page(struct ext4_inode_info *ei) > { > - *did_unlock = true; > up_write(&ei->i_mmap_sem); > schedule(); > down_write(&ei->i_mmap_sem); > @@ -4203,14 +4202,12 @@ int ext4_break_layouts(struct inode *inode) > { > struct ext4_inode_info *ei = EXT4_I(inode); > struct page *page; > - bool retry; > int error; > > if (WARN_ON_ONCE(!rwsem_is_locked(&ei->i_mmap_sem))) > return -EINVAL; > > do { > - retry = false; > page = dax_layout_busy_page(inode->i_mapping); > if (!page) > return 0; > @@ -4218,8 +4215,8 @@ int ext4_break_layouts(struct inode *inode) > error = ___wait_var_event(&page->_refcount, > atomic_read(&page->_refcount) == 1, > TASK_INTERRUPTIBLE, 0, 0, > - ext4_wait_dax_page(ei, &retry)); > - } while (error == 0 && retry); > + ext4_wait_dax_page(ei)); > + } while (error == 0); > > return error; > } >