| Message ID | 20171006211541.GA7409@bombadil.infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Acked-by: Johannes Thumshirn <jthumshirn@suse.de>
On Fri, 6 Oct 2017 14:15:41 -0700 Matthew Wilcox <willy@infradead.org> wrote: > When using FAT on a block device which supports rw_page, we can hit > BUG_ON(!PageLocked(page)) in try_to_free_buffers(). This is because we > call clean_buffers() after unlocking the page we've written. Introduce a > new clean_page_buffers() which cleans all buffers associated with a page > and call it from within bdev_write_page(). This is all pretty mature code (isn't it?). Any idea why this bug popped up now?
On Tue, Oct 10, 2017 at 12:44 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > > This is all pretty mature code (isn't it?). Any idea why this bug > popped up now? Also, while the patch looks sane, the clean_buffers(page, PAGE_SIZE); line really threw me. That's an insane value to pick, it looks like "bytes in page", but it isn't. It's just a random value that is bigger than "PAGE_SIZE >> SECTOR_SHIFT". I'd prefer to see just ~0u if the intention is just "bigger than anything possible". Linus
On Tue, Oct 10, 2017 at 01:31:44PM -0700, Linus Torvalds wrote: > On Tue, Oct 10, 2017 at 12:44 PM, Andrew Morton > <akpm@linux-foundation.org> wrote: > > > > This is all pretty mature code (isn't it?). Any idea why this bug > > popped up now? I have no idea why it's suddenly popped up. It looks like it should be a bohrbug, but it's actually a heisenbug, and I don't understand that either. > Also, while the patch looks sane, the > > clean_buffers(page, PAGE_SIZE); > > line really threw me. That's an insane value to pick, it looks like > "bytes in page", but it isn't. It's just a random value that is bigger > than "PAGE_SIZE >> SECTOR_SHIFT". > > I'd prefer to see just ~0u if the intention is just "bigger than > anything possible". Actually, I did choose it to be "number of bytes in the page", based on the reasoning that I didn't want to calculate what the actual block size was, and the block size surely couldn't be any smaller than one byte. I forgot about the SECTOR_SIZE limit on filesystem block size, so your spelling of "big enough" does look better. Now that I think about it some more, I suppose we might end up with a situation where we're eventually passing a hugepage to this routine, and futureproofing it with ~0U probably makes more sense.
diff --git a/fs/block_dev.c b/fs/block_dev.c index 9941dc8342df..3fbe75bdd257 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -716,10 +716,12 @@ int bdev_write_page(struct block_device *bdev, sector_t sector, set_page_writeback(page); result = ops->rw_page(bdev, sector + get_start_sect(bdev), page, true); - if (result) + if (result) { end_page_writeback(page); - else + } else { + clean_page_buffers(page); unlock_page(page); + } blk_queue_exit(bdev->bd_queue); return result; } diff --git a/fs/mpage.c b/fs/mpage.c index 2e4c41ccb5c9..d97b003f1607 100644 --- a/fs/mpage.c +++ b/fs/mpage.c @@ -468,6 +468,16 @@ static void clean_buffers(struct page *page, unsigned first_unmapped) try_to_free_buffers(page); } +/* + * For situations where we want to clean all buffers attached to a page. + * We don't need to calculate how many buffers are attached to the page, + * we just need to specify a number larger than the maximum number of buffers. + */ +void clean_page_buffers(struct page *page) +{ + clean_buffers(page, PAGE_SIZE); +} + static int __mpage_writepage(struct page *page, struct writeback_control *wbc, void *data) { @@ -605,10 +615,8 @@ static int __mpage_writepage(struct page *page, struct writeback_control *wbc, if (bio == NULL) { if (first_unmapped == blocks_per_page) { if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9), - page, wbc)) { - clean_buffers(page, first_unmapped); + page, wbc)) goto out; - } } bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9), BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH); diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index c8dae555eccf..446b24cac67d 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -232,6 +232,7 @@ int generic_write_end(struct file *, struct address_space *, loff_t, unsigned, unsigned, struct page *, void *); void page_zero_new_buffers(struct page *page, unsigned from, unsigned to); +void clean_page_buffers(struct page *page); int cont_write_begin(struct file *, struct address_space *, loff_t, unsigned, unsigned, struct page **, void **, get_block_t *, loff_t *);