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

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Message-ID: <715f636e-ff1b-301f-38a9-602437fdd95a@huawei.com>
Date:   Sun, 26 Sep 2021 19:35:01 +0800
From:   yangerkun <yangerkun@...wei.com>
To:     Theodore Ts'o <tytso@....edu>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Jan Kara <jack@...e.cz>
CC:     <yukuai3@...wei.com>
Subject: Re: [PATCH] ext4: if zeroout fails fall back to splitting the extent
 node

Hi,

Rethink about this problem. Should we consider other place which call 
ext4_issue_zeroout? Maybe it can trigger the problem too(in theory, not 
really happened)...

How about include follow patch which not only transfer ENOSPC to EIO. 
But also stop to overwrite the error return by ext4_ext_insert_extent in 
ext4_split_extent_at.

Besides, 308c57ccf431 ("ext4: if zeroout fails fall back to splitting 
the extent node") can work together with this patch.



diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c0de30f25185..66767ede235f 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3218,16 +3218,18 @@ static int ext4_split_extent_at(handle_t *handle,
                 goto out;

         if (EXT4_EXT_MAY_ZEROOUT & split_flag) {
+               int ret = 0;
+
                 if (split_flag & 
(EXT4_EXT_DATA_VALID1|EXT4_EXT_DATA_VALID2)) {
                         if (split_flag & EXT4_EXT_DATA_VALID1) {
-                               err = ext4_ext_zeroout(inode, ex2);
+                               ret = ext4_ext_zeroout(inode, ex2);
                                 zero_ex.ee_block = ex2->ee_block;
                                 zero_ex.ee_len = cpu_to_le16(
 
ext4_ext_get_actual_len(ex2));
                                 ext4_ext_store_pblock(&zero_ex,
 
ext4_ext_pblock(ex2));
                         } else {
-                               err = ext4_ext_zeroout(inode, ex);
+                               ret = ext4_ext_zeroout(inode, ex);
                                 zero_ex.ee_block = ex->ee_block;
                                 zero_ex.ee_len = cpu_to_le16(
 
ext4_ext_get_actual_len(ex));
@@ -3235,7 +3237,7 @@ static int ext4_split_extent_at(handle_t *handle,
                                                       ext4_ext_pblock(ex));
                         }
                 } else {
-                       err = ext4_ext_zeroout(inode, &orig_ex);
+                       ret = ext4_ext_zeroout(inode, &orig_ex);
                         zero_ex.ee_block = orig_ex.ee_block;
                         zero_ex.ee_len = cpu_to_le16(
 
ext4_ext_get_actual_len(&orig_ex));
@@ -3243,7 +3245,7 @@ static int ext4_split_extent_at(handle_t *handle,
                                               ext4_ext_pblock(&orig_ex));
                 }

-               if (!err) {
+               if (!ret) {
                         /* update the extent length and mark as 
initialized */
                         ex->ee_len = cpu_to_le16(ee_len);
                         ext4_ext_try_to_merge(handle, inode, path, ex);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d18852d6029c..95b970581864 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -427,6 +427,9 @@ int ext4_issue_zeroout(struct inode *inode, 
ext4_lblk_t lblk, ext4_fsblk_t pblk,
         if (ret > 0)
                 ret = 0;

+       if (ret == -ENOSPC)
+               ret = -EIO;
+
         return ret;
  }



在 2021/8/14 5:27, Theodore Ts'o 写道:
> 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)
>