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Subject[PATCH] iomap: Fix the write_count in iomap_add_to_ioend().
Date
From: Ritesh Harjani <riteshh@linux.ibm.com>

__bio_try_merge_page() may return same_page = 1 and merged = 0.
This could happen when bio->bi_iter.bi_size + len > UINT_MAX.
Handle this case in iomap_add_to_ioend() by incrementing write_count.
This scenario mostly happens where we have too much dirty data accumulated.

w/o the patch we hit below kernel warning,

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

Reported-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
---
fs/iomap/buffered-io.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index bcfc288dba3f..4e8062279e66 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1332,10 +1332,12 @@ iomap_add_to_ioend(struct inode *inode, loff_t offset, struct page *page,

merged = __bio_try_merge_page(wpc->ioend->io_bio, page, len, poff,
&same_page);
- if (iop && !same_page)
+ if (iop && merged && !same_page)
atomic_inc(&iop->write_count);

if (!merged) {
+ if (iop)
+ atomic_inc(&iop->write_count);
if (bio_full(wpc->ioend->io_bio, len)) {
wpc->ioend->io_bio =
iomap_chain_bio(wpc->ioend->io_bio);
--
2.25.4
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