linux-kernel - [PATCH 1/1] block: Set same_page to false in __bio_try_merge

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Message-Id: <e50582833c897c1a51a676d7726d1380a3e5a678.1598032711.git.riteshh@linux.ibm.com>
Date:   Fri, 21 Aug 2020 23:41:17 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     linux-block@...r.kernel.org
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, axboe@...nel.dk,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        Christoph Hellwig <hch@...radead.org>,
        Shivaprasad G Bhat <sbhat@...ux.ibm.com>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>
Subject: [PATCH 1/1] block: Set same_page to false in __bio_try_merge_page if ret is false

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@...radead.org>
Reported-by: Shivaprasad G Bhat <sbhat@...ux.ibm.com>
Signed-off-by: Anju T Sudhakar <anju@...ux.vnet.ibm.com>
Signed-off-by: Ritesh Harjani <riteshh@...ux.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