[PATCH 1/1] block: Set same_page to false in __bio_try_merge_page if ret is false

[PATCH 1/1] block: Set same_page to false in __bio_try_merge_page if ret is false

[Ritesh Harjani]

If we hit the UINT_MAX limit of bio->bi_iter.bi_size and so we are anyway
not merging this page in this bio, then it make sense to make same_page
also as false before returning.

Without this patch, we hit below WARNING in iomap.
This mostly happens with very large memory system and / or after tweaking
vm dirty threshold params to delay writeback of dirty data.

WARNING: CPU: 18 PID: 5130 at fs/iomap/buffered-io.c:74 iomap_page_release+0x120/0x150
 CPU: 18 PID: 5130 Comm: fio Kdump: loaded Tainted: G        W         5.8.0-rc3 #6
 Call Trace:
  __remove_mapping+0x154/0x320 (unreliable)
  iomap_releasepage+0x80/0x180
  try_to_release_page+0x94/0xe0
  invalidate_inode_page+0xc8/0x110
  invalidate_mapping_pages+0x1dc/0x540
  generic_fadvise+0x3c8/0x450
  xfs_file_fadvise+0x2c/0xe0 [xfs]
  vfs_fadvise+0x3c/0x60
  ksys_fadvise64_64+0x68/0xe0
  sys_fadvise64+0x28/0x40
  system_call_exception+0xf8/0x1c0
  system_call_common+0xf0/0x278

Suggested-by: Christoph Hellwig <hch@infradead.org>
Reported-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
---
[prev discussion]:- https://patchwork.kernel.org/patch/11723453/

 block/bio.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index a7366c02c9b5..675ecd81047b 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -877,8 +877,10 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
 		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
 
 		if (page_is_mergeable(bv, page, len, off, same_page)) {
-			if (bio->bi_iter.bi_size > UINT_MAX - len)
+			if (bio->bi_iter.bi_size > UINT_MAX - len) {
+				*same_page = false;
 				return false;
+			}
 			bv->bv_len += len;
 			bio->bi_iter.bi_size += len;
 			return true;
-- 
2.25.4

Re: [PATCH 1/1] block: Set same_page to false in __bio_try_merge_page if ret is false

[Ritesh Harjani]

Hello Jens,

On 8/21/20 11:41 PM, Ritesh Harjani wrote:
> If we hit the UINT_MAX limit of bio->bi_iter.bi_size and so we are anyway
> not merging this page in this bio, then it make sense to make same_page
> also as false before returning.
> 
> Without this patch, we hit below WARNING in iomap.
> This mostly happens with very large memory system and / or after tweaking
> vm dirty threshold params to delay writeback of dirty data.
> 
> WARNING: CPU: 18 PID: 5130 at fs/iomap/buffered-io.c:74 iomap_page_release+0x120/0x150
>   CPU: 18 PID: 5130 Comm: fio Kdump: loaded Tainted: G        W         5.8.0-rc3 #6
>   Call Trace:
>    __remove_mapping+0x154/0x320 (unreliable)
>    iomap_releasepage+0x80/0x180
>    try_to_release_page+0x94/0xe0
>    invalidate_inode_page+0xc8/0x110
>    invalidate_mapping_pages+0x1dc/0x540
>    generic_fadvise+0x3c8/0x450
>    xfs_file_fadvise+0x2c/0xe0 [xfs]
>    vfs_fadvise+0x3c/0x60
>    ksys_fadvise64_64+0x68/0xe0
>    sys_fadvise64+0x28/0x40
>    system_call_exception+0xf8/0x1c0
>    system_call_common+0xf0/0x278
> 
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Reported-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
> Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
> Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>

Sorry, I forgot to add the fixes tag. I think below commit
have introduced this. Let me know if you want me to
re-send this patch with below fixes tag.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cc90bc68422318eb8e75b15cd74bc8d538a7df29


-ritesh