Fix an incorrect number of pages being released for buffers that do not
start at the beginning of a page.
Fixes: 1b151e2435fc ("block: Remove special-casing of compound pages")
Cc: [email protected]
Signed-off-by: Tony Battersby <[email protected]>
---
Tested with 6.1.79. The 6.1 backport can just use
folio_put_refs(fi.folio, nr_pages) instead of do {...} while.
block/bio.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index b9642a41f286..b52b56067e79 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1152,7 +1152,7 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
bio_for_each_folio_all(fi, bio) {
struct page *page;
- size_t done = 0;
+ size_t nr_pages;
if (mark_dirty) {
folio_lock(fi.folio);
@@ -1160,10 +1160,11 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
folio_unlock(fi.folio);
}
page = folio_page(fi.folio, fi.offset / PAGE_SIZE);
+ nr_pages = (fi.offset + fi.length - 1) / PAGE_SIZE -
+ fi.offset / PAGE_SIZE + 1;
do {
bio_release_page(bio, page++);
- done += PAGE_SIZE;
- } while (done < fi.length);
+ } while (--nr_pages != 0);
}
}
EXPORT_SYMBOL_GPL(__bio_release_pages);
base-commit: d206a76d7d2726f3b096037f2079ce0bd3ba329b
--
2.25.1
On 2/29/24 14:53, Matthew Wilcox wrote:
> On Thu, Feb 29, 2024 at 01:08:09PM -0500, Tony Battersby wrote:
>> Fix an incorrect number of pages being released for buffers that do not
>> start at the beginning of a page.
> Oh, I see what I did. Wouldn't a simpler fix be to just set "done" to
> offset_in_page(fi.offset)?
Actually it would be:
ssize_t done = -offset_in_page(offset);
But then you have signed vs. unsigned comparison in the while(), or you
could rearrange the loop to avoid the negative, but then it gets clunky.
>
>> @@ -1152,7 +1152,7 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
>>
>> bio_for_each_folio_all(fi, bio) {
>> struct page *page;
>> - size_t done = 0;
>> + size_t nr_pages;
>>
>> if (mark_dirty) {
>> folio_lock(fi.folio);
>> @@ -1160,10 +1160,11 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
>> folio_unlock(fi.folio);
>> }
>> page = folio_page(fi.folio, fi.offset / PAGE_SIZE);
>> + nr_pages = (fi.offset + fi.length - 1) / PAGE_SIZE -
>> + fi.offset / PAGE_SIZE + 1;
>> do {
>> bio_release_page(bio, page++);
>> - done += PAGE_SIZE;
>> - } while (done < fi.length);
>> + } while (--nr_pages != 0);
>> }
>> }
>> EXPORT_SYMBOL_GPL(__bio_release_pages);
> The long-term path here, I think, is to replace this bio_release_page()
> with a bio_release_folio(folio, offset, length) which calls into
> a new unpin_user_folio(folio, nr) which calls gup_put_folio().
I developed the patch with the 6.1 stable series, which just has:
nr_pages = (fi.offset + fi.length - 1) / PAGE_SIZE -
fi.offset / PAGE_SIZE + 1;
folio_put_refs(fi.folio, nr_pages);
Which is another reason that I went for the direct nr_pages
calculation. Would you still prefer the negative offset_in_page() approach?
Tony
On Thu, Feb 29, 2024 at 01:08:09PM -0500, Tony Battersby wrote:
> Fix an incorrect number of pages being released for buffers that do not
> start at the beginning of a page.
>
> Fixes: 1b151e2435fc ("block: Remove special-casing of compound pages")
> Cc: [email protected]
> Signed-off-by: Tony Battersby <[email protected]>
> ---
This resolves the QEMU hugetlb issue I noted earlier today here [1].
I tested it on 6.1.79, 6.8-rc6 and linux-next-20240229. Thank you!
Feel free to add a:
Tested-by: Greg Edwards <[email protected]>
[1] https://lore.kernel.org/linux-block/[email protected]/
On Thu, Feb 29, 2024 at 01:08:09PM -0500, Tony Battersby wrote:
> Fix an incorrect number of pages being released for buffers that do not
> start at the beginning of a page.
Oh, I see what I did. Wouldn't a simpler fix be to just set "done" to
offset_in_page(fi.offset)?
> @@ -1152,7 +1152,7 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
>
> bio_for_each_folio_all(fi, bio) {
> struct page *page;
> - size_t done = 0;
> + size_t nr_pages;
>
> if (mark_dirty) {
> folio_lock(fi.folio);
> @@ -1160,10 +1160,11 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
> folio_unlock(fi.folio);
> }
> page = folio_page(fi.folio, fi.offset / PAGE_SIZE);
> + nr_pages = (fi.offset + fi.length - 1) / PAGE_SIZE -
> + fi.offset / PAGE_SIZE + 1;
> do {
> bio_release_page(bio, page++);
> - done += PAGE_SIZE;
> - } while (done < fi.length);
> + } while (--nr_pages != 0);
> }
> }
> EXPORT_SYMBOL_GPL(__bio_release_pages);
The long-term path here, I think, is to replace this bio_release_page()
with a bio_release_folio(folio, offset, length) which calls into
a new unpin_user_folio(folio, nr) which calls gup_put_folio().
On 2/29/24 17:56, Greg Edwards wrote:
> On Thu, Feb 29, 2024 at 01:08:09PM -0500, Tony Battersby wrote:
>> Fix an incorrect number of pages being released for buffers that do not
>> start at the beginning of a page.
>>
>> Fixes: 1b151e2435fc ("block: Remove special-casing of compound pages")
>> Cc: [email protected]
>> Signed-off-by: Tony Battersby <[email protected]>
>> ---
> This resolves the QEMU hugetlb issue I noted earlier today here [1].
> I tested it on 6.1.79, 6.8-rc6 and linux-next-20240229. Thank you!
>
> Feel free to add a:
>
> Tested-by: Greg Edwards <[email protected]>
>
> [1] https://lore.kernel.org/linux-block/[email protected]/
Jens, can I get this added to 6.8 (or 6.9 if it is too late)?
Thanks,
Tony
On 3/6/24 8:03 AM, Tony Battersby wrote:
> On 2/29/24 17:56, Greg Edwards wrote:
>> On Thu, Feb 29, 2024 at 01:08:09PM -0500, Tony Battersby wrote:
>>> Fix an incorrect number of pages being released for buffers that do not
>>> start at the beginning of a page.
>>>
>>> Fixes: 1b151e2435fc ("block: Remove special-casing of compound pages")
>>> Cc: [email protected]
>>> Signed-off-by: Tony Battersby <[email protected]>
>>> ---
>> This resolves the QEMU hugetlb issue I noted earlier today here [1].
>> I tested it on 6.1.79, 6.8-rc6 and linux-next-20240229. Thank you!
>>
>> Feel free to add a:
>>
>> Tested-by: Greg Edwards <[email protected]>
>>
>> [1] https://lore.kernel.org/linux-block/[email protected]/
>
> Jens, can I get this added to 6.8 (or 6.9 if it is too late)?
Let's just go for 6.9 at this pount, we're almost there. I'll queue it
up.
--
Jens Axboe
On Thu, 29 Feb 2024 13:08:09 -0500, Tony Battersby wrote:
> Fix an incorrect number of pages being released for buffers that do not
> start at the beginning of a page.
>
>
Applied, thanks!
[1/1] block: Fix page refcounts for unaligned buffers in __bio_release_pages()
commit: 38b43539d64b2fa020b3b9a752a986769f87f7a6
Best regards,
--
Jens Axboe