From: Dave Jiang Subject: [PATCH 1/2] ext4: Close race between direct IO and ext4_break_layouts() Date: Tue, 07 Aug 2018 15:11:37 -0700 Message-ID: <153367989755.37314.6889218648604435494.stgit@djiang5-desk3.ch.intel.com> 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: 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: 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 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. Note that this works around the race exposed by my unit test, but I think that there is another race that needs to be addressed, probably with additional synchronization added between direct I/O and {ext4,xfs}_break_layouts(). Signed-off-by: Ross Zwisler Reviewed-by: Jan Kara --- 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; }