From 0e499890c1fd9e0a1bed02002161c4c7873d7489 Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Wed, 18 May 2011 13:55:20 -0400 Subject: [PATCH] ext4: wait for writeback to complete while making pages writable In order to stabilize pages during disk writes, ext4_page_mkwrite must wait for writeback operations to complete before making a page writable. Furthermore, the function must return locked pages, and recheck the writeback status if the page lock is ever dropped. The "someone could wander in" part of this patch was suggested by Chris Mason. Signed-off-by: Darrick J. Wong Signed-off-by: "Theodore Ts'o" --- fs/ext4/inode.c | 24 +++++++++++++++++++----- 1 file changed, 19 insertions(+), 5 deletions(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index f6caaac83731..6348c1f610c2 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -5809,15 +5809,19 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) goto out_unlock; } ret = 0; - if (PageMappedToDisk(page)) - goto out_unlock; + + lock_page(page); + wait_on_page_writeback(page); + if (PageMappedToDisk(page)) { + up_read(&inode->i_alloc_sem); + return VM_FAULT_LOCKED; + } if (page->index == size >> PAGE_CACHE_SHIFT) len = size & ~PAGE_CACHE_MASK; else len = PAGE_CACHE_SIZE; - lock_page(page); /* * return if we have all the buffers mapped. This avoid * the need to call write_begin/write_end which does a @@ -5827,8 +5831,8 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) if (page_has_buffers(page)) { if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL, ext4_bh_unmapped)) { - unlock_page(page); - goto out_unlock; + up_read(&inode->i_alloc_sem); + return VM_FAULT_LOCKED; } } unlock_page(page); @@ -5848,6 +5852,16 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) if (ret < 0) goto out_unlock; ret = 0; + + /* + * write_begin/end might have created a dirty page and someone + * could wander in and start the IO. Make sure that hasn't + * happened. + */ + lock_page(page); + wait_on_page_writeback(page); + up_read(&inode->i_alloc_sem); + return VM_FAULT_LOCKED; out_unlock: if (ret) ret = VM_FAULT_SIGBUS;