linux-kernel - Re: [PATCH v2 3/9] mm: clear any AS_* errors when returning error on any fsync or close

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Date:   Thu, 09 Mar 2017 08:23:43 +1100
From:   NeilBrown <neilb@...e.com>
To:     Jeff Layton <jlayton@...hat.com>, viro@...iv.linux.org.uk,
        akpm@...ux-foundation.org
Cc:     konishi.ryusuke@....ntt.co.jp, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-nilfs@...r.kernel.org, ross.zwisler@...ux.intel.com,
        jack@...e.cz, openosd@...il.com, adilger@...ger.ca,
        James.Bottomley@...senPartnership.com
Subject: Re: [PATCH v2 3/9] mm: clear any AS_* errors when returning error on any fsync or close

On Thu, Mar 09 2017, Jeff Layton wrote:

> Currently we don't clear the address space error when there is a -EIO
> error on fsynci, due to writeback initiation failure. If writes fail
> with -EIO and the mapping is flagged with an AS_EIO or AS_ENOSPC error,
> then we can end up returning errors on two fsync calls, even when a
> write between them succeeded (or there was no write).
>
> Ensure that we also clear out any mapping errors when initiating
> writeback fails with -EIO in filemap_write_and_wait and
> filemap_write_and_wait_range.

This change appears to assume that filemap_write_and_wait* is only
called from fsync() (or similar) and the return status is always
checked.

A __must_check annotation might be helpful.

It would catch v9_fs_file_lock(), afs_setattr() and others.

While I think your change is probably heading in the right direction,
there seem to be some loose ends still.

Thanks,
NeilBrown


>
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Jeff Layton <jlayton@...hat.com>
> ---
>  mm/filemap.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 1694623a6289..fc123b9833e1 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -488,7 +488,7 @@ EXPORT_SYMBOL(filemap_fdatawait);
>  
>  int filemap_write_and_wait(struct address_space *mapping)
>  {
> -	int err = 0;
> +	int err;
>  
>  	if ((!dax_mapping(mapping) && mapping->nrpages) ||
>  	    (dax_mapping(mapping) && mapping->nrexceptional)) {
> @@ -499,10 +499,18 @@ int filemap_write_and_wait(struct address_space *mapping)
>  		 * But the -EIO is special case, it may indicate the worst
>  		 * thing (e.g. bug) happened, so we avoid waiting for it.
>  		 */
> -		if (err != -EIO) {
> +		if (likely(err != -EIO)) {
>  			int err2 = filemap_fdatawait(mapping);
>  			if (!err)
>  				err = err2;
> +		} else {
> +			/*
> +			 * Clear the error in the address space since we're
> +			 * returning an error here. -EIO takes precedence over
> +			 * everything else though, so we can just discard
> +			 * the return here.
> +			 */
> +			filemap_check_errors(mapping);
>  		}
>  	} else {
>  		err = filemap_check_errors(mapping);
> @@ -537,6 +545,14 @@ int filemap_write_and_wait_range(struct address_space *mapping,
>  						lstart, lend);
>  			if (!err)
>  				err = err2;
> +		} else {
> +			/*
> +			 * Clear the error in the address space since we're
> +			 * returning an error here. -EIO takes precedence over
> +			 * everything else though, so we can just discard
> +			 * the return here.
> +			 */
> +			filemap_check_errors(mapping);
>  		}
>  	} else {
>  		err = filemap_check_errors(mapping);
> -- 
> 2.9.3

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