linux-ext4 - [PATCH] ext4: if zeroout fails fall back to splitting the extent node

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Message-Id: <20210813212701.366447-1-tytso@mit.edu>
Date:   Fri, 13 Aug 2021 17:27:01 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     "Theodore Ts'o" <tytso@....edu>, yangerkun@...wei.com,
        yukuai3@...wei.com
Subject: [PATCH] ext4: if zeroout fails fall back to splitting the extent node

If the underlying storage device is using thin-provisioning, it's
possible for a zeroout operation to return ENOSPC.

Commit df22291ff0fd ("ext4: Retry block allocation if we have free blocks
left") added logic to retry block allocation since we might get free block
after we commit a transaction. But the ENOSPC from thin-provisioning
will confuse ext4, and lead to an infinite loop.

Since using zeroout instead of splitting the extent node is an
optimization, if it fails, we might as well fall back to splitting the
extent node.

Reported-by: yangerkun <yangerkun@...wei.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
---

I've run this through my battery of tests, and it doesn't cause any
regressions.  Yangerkun, can you test this and see if this works for
you?

 fs/ext4/extents.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 92ad64b89d9b..501516cadc1b 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3569,7 +3569,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 				split_map.m_len - ee_block);
 			err = ext4_ext_zeroout(inode, &zero_ex1);
 			if (err)
-				goto out;
+				goto fallback;
 			split_map.m_len = allocated;
 		}
 		if (split_map.m_lblk - ee_block + split_map.m_len <
@@ -3583,7 +3583,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 						      ext4_ext_pblock(ex));
 				err = ext4_ext_zeroout(inode, &zero_ex2);
 				if (err)
-					goto out;
+					goto fallback;
 			}

 			split_map.m_len += split_map.m_lblk - ee_block;
@@ -3592,6 +3592,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 		}
 	}

+fallback:
 	err = ext4_split_extent(handle, inode, ppath, &split_map, split_flag,
 				flags);
 	if (err > 0)
-- 
2.31.0