Re: [PATCH v5 08/17] dax: set errors in mapping when writeback fails

[Jeff Layton]

On Mon, 2017-06-05 at 19:01 -0600, Ross Zwisler wrote:
> On Wed, May 31, 2017 at 08:45:31AM -0400, Jeff Layton wrote:
> > Jan's description for this patch is much better than mine, so I'm
> > quoting it verbatim here:
> > 
> > -8<-
> > DAX currently doesn't set errors in the mapping when cache flushing
> > fails in dax_writeback_mapping_range(). Since this function can get
> > called only from fsync(2) or sync(2), this is actually as good as it can
> > currently get since we correctly propagate the error up from
> > dax_writeback_mapping_range() to filemap_fdatawrite()
> > 
> > However, in the future better writeback error handling will enable us to
> > properly report these errors on fsync(2) even if there are multiple file
> > descriptors open against the file or if sync(2) gets called before
> > fsync(2). So convert DAX to using standard error reporting through the
> > mapping.
> > -8<-
> > 
> > For now, only do this when the FS_WB_ERRSEQ flag is set. The
> > AS_EIO/AS_ENOSPC flags are not currently cleared in the older code when
> > writeback initiation fails, only when we discover an error after waiting
> > on writeback to complete, so we only want to do this with errseq_t based
> > error handling to prevent seeing duplicate errors on fsync.
> > 
> > Signed-off-by: Jeff Layton 
> > Reviewed-by: Jan Kara 
> > Reviewed-by: Christoph Hellwig 
> > Reviewed-and-Tested-by: Ross Zwisler 
> 
> Re-tested this version of the series with some injected DAX errors, and it
> looks good.

Excellent! Thanks very much for helping test it.

-- 
Jeff Layton 
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Re: [PATCH v5 08/17] dax: set errors in mapping when writeback fails

[Ross Zwisler]

On Wed, May 31, 2017 at 08:45:31AM -0400, Jeff Layton wrote:
> Jan's description for this patch is much better than mine, so I'm
> quoting it verbatim here:
> 
> -8<-
> DAX currently doesn't set errors in the mapping when cache flushing
> fails in dax_writeback_mapping_range(). Since this function can get
> called only from fsync(2) or sync(2), this is actually as good as it can
> currently get since we correctly propagate the error up from
> dax_writeback_mapping_range() to filemap_fdatawrite()
> 
> However, in the future better writeback error handling will enable us to
> properly report these errors on fsync(2) even if there are multiple file
> descriptors open against the file or if sync(2) gets called before
> fsync(2). So convert DAX to using standard error reporting through the
> mapping.
> -8<-
> 
> For now, only do this when the FS_WB_ERRSEQ flag is set. The
> AS_EIO/AS_ENOSPC flags are not currently cleared in the older code when
> writeback initiation fails, only when we discover an error after waiting
> on writeback to complete, so we only want to do this with errseq_t based
> error handling to prevent seeing duplicate errors on fsync.
> 
> Signed-off-by: Jeff Layton 
> Reviewed-by: Jan Kara 
> Reviewed-by: Christoph Hellwig 
> Reviewed-and-Tested-by: Ross Zwisler 

Re-tested this version of the series with some injected DAX errors, and it
looks good.
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[PATCH v5 08/17] dax: set errors in mapping when writeback fails

[Jeff Layton]

Jan's description for this patch is much better than mine, so I'm
quoting it verbatim here:

-8<-
DAX currently doesn't set errors in the mapping when cache flushing
fails in dax_writeback_mapping_range(). Since this function can get
called only from fsync(2) or sync(2), this is actually as good as it can
currently get since we correctly propagate the error up from
dax_writeback_mapping_range() to filemap_fdatawrite()

However, in the future better writeback error handling will enable us to
properly report these errors on fsync(2) even if there are multiple file
descriptors open against the file or if sync(2) gets called before
fsync(2). So convert DAX to using standard error reporting through the
mapping.
-8<-

For now, only do this when the FS_WB_ERRSEQ flag is set. The
AS_EIO/AS_ENOSPC flags are not currently cleared in the older code when
writeback initiation fails, only when we discover an error after waiting
on writeback to complete, so we only want to do this with errseq_t based
error handling to prevent seeing duplicate errors on fsync.

Signed-off-by: Jeff Layton 
Reviewed-by: Jan Kara 
Reviewed-by: Christoph Hellwig 
Reviewed-and-Tested-by: Ross Zwisler 
---
 fs/dax.c | 18 +-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index c22eaf162f95..42788d8505c7 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -856,8 +856,24 @@ int dax_writeback_mapping_range(struct address_space 
*mapping,
 
ret = dax_writeback_one(bdev, dax_dev, mapping,
indices[i], pvec.pages[i]);
-   if (ret < 0)
+   if (ret < 0) {
+   /*
+* For fs' that use errseq_t based error
+* tracking, we must call mapping_set_error
+* here to ensure that fsync on all open fds
+* get back an error. Doing this with the old
+* wb error tracking infrastructure is
+* problematic though, as DAX writeback is
+* synchronous, and the error flags are not
+* cleared when initiation fails, only when
+* it fails after the write has been submitted
+* to the backing store.
+*/
+   if (mapping->host->i_sb->s_type->fs_flags &
+   FS_WB_ERRSEQ)
+   mapping_set_error(mapping, ret);
goto out;
+   }
}
}
 out:
-- 
2.9.4

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