Re: [PATCH] Fix mpage_writepage() for pages with buffers

2017-10-11 Thread Matthew Wilcox 
On Tue, Oct 10, 2017 at 01:31:44PM -0700, Linus Torvalds wrote:
> On Tue, Oct 10, 2017 at 12:44 PM, Andrew Morton
>  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.
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Re: [PATCH] Fix mpage_writepage() for pages with buffers

2017-10-10 Thread Linus Torvalds 
On Tue, Oct 10, 2017 at 12:44 PM, Andrew Morton
 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
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Re: [PATCH] Fix mpage_writepage() for pages with buffers

2017-10-10 Thread Andrew Morton 
On Fri, 6 Oct 2017 14:15:41 -0700 Matthew Wilcox  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?

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Re: [PATCH] Fix mpage_writepage() for pages with buffers

2017-10-09 Thread Johannes Thumshirn 

Acked-by: Johannes Thumshirn 
-- 
Johannes Thumshirn  Storage
jthumsh...@suse.de+49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
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[PATCH] Fix mpage_writepage() for pages with buffers

2017-10-06 Thread Matthew Wilcox 

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().

Reported-by: Toshi Kani 
Reported-by: OGAWA Hirofumi 
Tested-by: Toshi Kani 
Signed-off-by: Matthew Wilcox 
Cc: sta...@vger.kernel.org

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 *);
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