Re: [PATCH v7 05/22] jbd2: don't clear and reset errors after waiting on writeback

[Carlos Maiolino]

On Fri, Jun 16, 2017 at 03:34:10PM -0400, Jeff Layton wrote:
> Resetting this flag is almost certainly racy, and will be problematic
> with some coming changes.
> 
> Make filemap_fdatawait_keep_errors return int, but not clear the flag(s).
> Have jbd2 call it instead of filemap_fdatawait and don't attempt to
> re-set the error flag if it fails.
> 
> Signed-off-by: Jeff Layton 
> ---
>  fs/jbd2/commit.c   | 15 +++
>  include/linux/fs.h |  2 +-
>  mm/filemap.c   | 16 ++--
>  3 files changed, 18 insertions(+), 15 deletions(-)
> 
I'm not too experienced with jbd2 internals, but this patch is clear enough:

Reviewed-by: Carlos Maiolino 

-- 
Carlos

Re: [PATCH v7 05/22] jbd2: don't clear and reset errors after waiting on writeback

[Jan Kara]

On Fri 16-06-17 15:34:10, Jeff Layton wrote:
> Resetting this flag is almost certainly racy, and will be problematic
> with some coming changes.
> 
> Make filemap_fdatawait_keep_errors return int, but not clear the flag(s).
> Have jbd2 call it instead of filemap_fdatawait and don't attempt to
> re-set the error flag if it fails.
> 
> Signed-off-by: Jeff Layton 

Looks good to me. You can add:

Reviewed-by: Jan Kara 

Honza

> ---
>  fs/jbd2/commit.c   | 15 +++
>  include/linux/fs.h |  2 +-
>  mm/filemap.c   | 16 ++--
>  3 files changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index b6b194ec1b4f..502110540598 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -263,18 +263,9 @@ static int journal_finish_inode_data_buffers(journal_t 
> *journal,
>   continue;
>   jinode->i_flags |= JI_COMMIT_RUNNING;
>   spin_unlock(>j_list_lock);
> - err = filemap_fdatawait(jinode->i_vfs_inode->i_mapping);
> - if (err) {
> - /*
> -  * Because AS_EIO is cleared by
> -  * filemap_fdatawait_range(), set it again so
> -  * that user process can get -EIO from fsync().
> -  */
> - mapping_set_error(jinode->i_vfs_inode->i_mapping, -EIO);
> -
> - if (!ret)
> - ret = err;
> - }
> + err = 
> filemap_fdatawait_keep_errors(jinode->i_vfs_inode->i_mapping);
> + if (!ret)
> + ret = err;
>   spin_lock(>j_list_lock);
>   jinode->i_flags &= ~JI_COMMIT_RUNNING;
>   smp_mb();
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 1a135274b4f8..1b1233a1db1e 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2509,7 +2509,7 @@ extern int write_inode_now(struct inode *, int);
>  extern int filemap_fdatawrite(struct address_space *);
>  extern int filemap_flush(struct address_space *);
>  extern int filemap_fdatawait(struct address_space *);
> -extern void filemap_fdatawait_keep_errors(struct address_space *);
> +extern int filemap_fdatawait_keep_errors(struct address_space *);
>  extern int filemap_fdatawait_range(struct address_space *, loff_t lstart,
>  loff_t lend);
>  extern int filemap_write_and_wait(struct address_space *mapping);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index b9e870600572..37f286df7c95 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -311,6 +311,16 @@ int filemap_check_errors(struct address_space *mapping)
>  }
>  EXPORT_SYMBOL(filemap_check_errors);
>  
> +static int filemap_check_and_keep_errors(struct address_space *mapping)
> +{
> + /* Check for outstanding write errors */
> + if (test_bit(AS_EIO, >flags))
> + return -EIO;
> + if (test_bit(AS_ENOSPC, >flags))
> + return -ENOSPC;
> + return 0;
> +}
> +
>  /**
>   * __filemap_fdatawrite_range - start writeback on mapping dirty pages in 
> range
>   * @mapping: address space structure to write
> @@ -455,15 +465,17 @@ EXPORT_SYMBOL(filemap_fdatawait_range);
>   * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
>   * fsfreeze(8)
>   */
> -void filemap_fdatawait_keep_errors(struct address_space *mapping)
> +int filemap_fdatawait_keep_errors(struct address_space *mapping)
>  {
>   loff_t i_size = i_size_read(mapping->host);
>  
>   if (i_size == 0)
> - return;
> + return 0;
>  
>   __filemap_fdatawait_range(mapping, 0, i_size - 1);
> + return filemap_check_and_keep_errors(mapping);
>  }
> +EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
>  
>  /**
>   * filemap_fdatawait - wait for all under-writeback pages to complete
> -- 
> 2.13.0
> 
-- 
Jan Kara 
SUSE Labs, CR

[PATCH v7 05/22] jbd2: don't clear and reset errors after waiting on writeback

[Jeff Layton]

Resetting this flag is almost certainly racy, and will be problematic
with some coming changes.

Make filemap_fdatawait_keep_errors return int, but not clear the flag(s).
Have jbd2 call it instead of filemap_fdatawait and don't attempt to
re-set the error flag if it fails.

Signed-off-by: Jeff Layton 
---
 fs/jbd2/commit.c   | 15 +++
 include/linux/fs.h |  2 +-
 mm/filemap.c   | 16 ++--
 3 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index b6b194ec1b4f..502110540598 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -263,18 +263,9 @@ static int journal_finish_inode_data_buffers(journal_t 
*journal,
continue;
jinode->i_flags |= JI_COMMIT_RUNNING;
spin_unlock(>j_list_lock);
-   err = filemap_fdatawait(jinode->i_vfs_inode->i_mapping);
-   if (err) {
-   /*
-* Because AS_EIO is cleared by
-* filemap_fdatawait_range(), set it again so
-* that user process can get -EIO from fsync().
-*/
-   mapping_set_error(jinode->i_vfs_inode->i_mapping, -EIO);
-
-   if (!ret)
-   ret = err;
-   }
+   err = 
filemap_fdatawait_keep_errors(jinode->i_vfs_inode->i_mapping);
+   if (!ret)
+   ret = err;
spin_lock(>j_list_lock);
jinode->i_flags &= ~JI_COMMIT_RUNNING;
smp_mb();
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1a135274b4f8..1b1233a1db1e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2509,7 +2509,7 @@ extern int write_inode_now(struct inode *, int);
 extern int filemap_fdatawrite(struct address_space *);
 extern int filemap_flush(struct address_space *);
 extern int filemap_fdatawait(struct address_space *);
-extern void filemap_fdatawait_keep_errors(struct address_space *);
+extern int filemap_fdatawait_keep_errors(struct address_space *);
 extern int filemap_fdatawait_range(struct address_space *, loff_t lstart,
   loff_t lend);
 extern int filemap_write_and_wait(struct address_space *mapping);
diff --git a/mm/filemap.c b/mm/filemap.c
index b9e870600572..37f286df7c95 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -311,6 +311,16 @@ int filemap_check_errors(struct address_space *mapping)
 }
 EXPORT_SYMBOL(filemap_check_errors);
 
+static int filemap_check_and_keep_errors(struct address_space *mapping)
+{
+   /* Check for outstanding write errors */
+   if (test_bit(AS_EIO, >flags))
+   return -EIO;
+   if (test_bit(AS_ENOSPC, >flags))
+   return -ENOSPC;
+   return 0;
+}
+
 /**
  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
  * @mapping:   address space structure to write
@@ -455,15 +465,17 @@ EXPORT_SYMBOL(filemap_fdatawait_range);
  * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
  * fsfreeze(8)
  */
-void filemap_fdatawait_keep_errors(struct address_space *mapping)
+int filemap_fdatawait_keep_errors(struct address_space *mapping)
 {
loff_t i_size = i_size_read(mapping->host);
 
if (i_size == 0)
-   return;
+   return 0;
 
__filemap_fdatawait_range(mapping, 0, i_size - 1);
+   return filemap_check_and_keep_errors(mapping);
 }
+EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
 
 /**
  * filemap_fdatawait - wait for all under-writeback pages to complete
-- 
2.13.0