On Fri 07-11-14 13:31:59, gregkh@xxxxxxxxxxxxxxxxxxx wrote: > > This is a note to let you know that I've just added the patch titled > > vfs: fix data corruption when blocksize < pagesize for mmaped data > > to the 3.17-stable tree which can be found at: > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary > > The filename of the patch is: > vfs-fix-data-corruption-when-blocksize-pagesize-for-mmaped-data.patch > and it can be found in the queue-3.17 subdirectory. > > If you, or anyone else, feels it should not be added to the stable tree, > please let <stable@xxxxxxxxxxxxxxx> know about it. Greg, this patch needs also a patch f55fefd1a5a339b1bd08c120b93312d6eb64a9fb on top of it so that XFS doesn't spew false warnings. It's harmless but rather annoying. I forgot to tag it for stable. Sorry. Honza > From 90a8020278c1598fafd071736a0846b38510309c Mon Sep 17 00:00:00 2001 > From: Jan Kara <jack@xxxxxxx> > Date: Wed, 1 Oct 2014 21:49:18 -0400 > Subject: vfs: fix data corruption when blocksize < pagesize for mmaped data > > From: Jan Kara <jack@xxxxxxx> > > commit 90a8020278c1598fafd071736a0846b38510309c upstream. > > ->page_mkwrite() is used by filesystems to allocate blocks under a page > which is becoming writeably mmapped in some process' address space. This > allows a filesystem to return a page fault if there is not enough space > available, user exceeds quota or similar problem happens, rather than > silently discarding data later when writepage is called. > > However VFS fails to call ->page_mkwrite() in all the cases where > filesystems need it when blocksize < pagesize. For example when > blocksize = 1024, pagesize = 4096 the following is problematic: > ftruncate(fd, 0); > pwrite(fd, buf, 1024, 0); > map = mmap(NULL, 1024, PROT_WRITE, MAP_SHARED, fd, 0); > map[0] = 'a'; ----> page_mkwrite() for index 0 is called > ftruncate(fd, 10000); /* or even pwrite(fd, buf, 1, 10000) */ > mremap(map, 1024, 10000, 0); > map[4095] = 'a'; ----> no page_mkwrite() called > > At the moment ->page_mkwrite() is called, filesystem can allocate only > one block for the page because i_size == 1024. Otherwise it would create > blocks beyond i_size which is generally undesirable. But later at > ->writepage() time, we also need to store data at offset 4095 but we > don't have block allocated for it. > > This patch introduces a helper function filesystems can use to have > ->page_mkwrite() called at all the necessary moments. > > Signed-off-by: Jan Kara <jack@xxxxxxx> > Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > --- > fs/buffer.c | 3 ++ > include/linux/mm.h | 1 > mm/truncate.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 61 insertions(+) > > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -2082,6 +2082,7 @@ int generic_write_end(struct file *file, > struct page *page, void *fsdata) > { > struct inode *inode = mapping->host; > + loff_t old_size = inode->i_size; > int i_size_changed = 0; > > copied = block_write_end(file, mapping, pos, len, copied, page, fsdata); > @@ -2101,6 +2102,8 @@ int generic_write_end(struct file *file, > unlock_page(page); > page_cache_release(page); > > + if (old_size < pos) > + pagecache_isize_extended(inode, old_size, pos); > /* > * Don't mark the inode dirty under page lock. First, it unnecessarily > * makes the holding time of page lock longer. Second, it forces lock > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1174,6 +1174,7 @@ static inline void unmap_shared_mapping_ > > extern void truncate_pagecache(struct inode *inode, loff_t new); > extern void truncate_setsize(struct inode *inode, loff_t newsize); > +void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to); > void truncate_pagecache_range(struct inode *inode, loff_t offset, loff_t end); > int truncate_inode_page(struct address_space *mapping, struct page *page); > int generic_error_remove_page(struct address_space *mapping, struct page *page); > --- a/mm/truncate.c > +++ b/mm/truncate.c > @@ -20,6 +20,7 @@ > #include <linux/buffer_head.h> /* grr. try_to_release_page, > do_invalidatepage */ > #include <linux/cleancache.h> > +#include <linux/rmap.h> > #include "internal.h" > > static void clear_exceptional_entry(struct address_space *mapping, > @@ -719,12 +720,68 @@ EXPORT_SYMBOL(truncate_pagecache); > */ > void truncate_setsize(struct inode *inode, loff_t newsize) > { > + loff_t oldsize = inode->i_size; > + > i_size_write(inode, newsize); > + if (newsize > oldsize) > + pagecache_isize_extended(inode, oldsize, newsize); > truncate_pagecache(inode, newsize); > } > EXPORT_SYMBOL(truncate_setsize); > > /** > + * pagecache_isize_extended - update pagecache after extension of i_size > + * @inode: inode for which i_size was extended > + * @from: original inode size > + * @to: new inode size > + * > + * Handle extension of inode size either caused by extending truncate or by > + * write starting after current i_size. We mark the page straddling current > + * i_size RO so that page_mkwrite() is called on the nearest write access to > + * the page. This way filesystem can be sure that page_mkwrite() is called on > + * the page before user writes to the page via mmap after the i_size has been > + * changed. > + * > + * The function must be called after i_size is updated so that page fault > + * coming after we unlock the page will already see the new i_size. > + * The function must be called while we still hold i_mutex - this not only > + * makes sure i_size is stable but also that userspace cannot observe new > + * i_size value before we are prepared to store mmap writes at new inode size. > + */ > +void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to) > +{ > + int bsize = 1 << inode->i_blkbits; > + loff_t rounded_from; > + struct page *page; > + pgoff_t index; > + > + WARN_ON(!mutex_is_locked(&inode->i_mutex)); > + WARN_ON(to > inode->i_size); > + > + if (from >= to || bsize == PAGE_CACHE_SIZE) > + return; > + /* Page straddling @from will not have any hole block created? */ > + rounded_from = round_up(from, bsize); > + if (to <= rounded_from || !(rounded_from & (PAGE_CACHE_SIZE - 1))) > + return; > + > + index = from >> PAGE_CACHE_SHIFT; > + page = find_lock_page(inode->i_mapping, index); > + /* Page not cached? Nothing to do */ > + if (!page) > + return; > + /* > + * See clear_page_dirty_for_io() for details why set_page_dirty() > + * is needed. > + */ > + if (page_mkclean(page)) > + set_page_dirty(page); > + unlock_page(page); > + page_cache_release(page); > +} > +EXPORT_SYMBOL(pagecache_isize_extended); > + > +/** > * truncate_pagecache_range - unmap and remove pagecache that is hole-punched > * @inode: inode > * @lstart: offset of beginning of hole > > > Patches currently in stable-queue which might be from jack@xxxxxxx are > > queue-3.17/vfs-fix-data-corruption-when-blocksize-pagesize-for-mmaped-data.patch -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html