diff mbox series

netfs: Fix the pre-flush when appending to a file in writethrough mode

Message ID 2150448.1714130115@warthog.procyon.org.uk (mailing list archive)
State New
Headers show
Series netfs: Fix the pre-flush when appending to a file in writethrough mode | expand

Commit Message

David Howells April 26, 2024, 11:15 a.m. UTC
In netfs_perform_write(), when the file is marked NETFS_ICTX_WRITETHROUGH
or O_*SYNC or RWF_*SYNC was specified, write-through caching is performed
on a buffered file.  When setting up for write-through, we flush any
conflicting writes in the region and wait for the write to complete,
failing if there's a write error to return.

The issue arises if we're writing at or above the EOF position because we
skip the flush and - more importantly - the wait.  This becomes a problem
if there's a partial folio at the end of the file that is being written out
and we want to make a write to it too.  Both the already-running write and
the write we start both want to clear the writeback mark, but whoever is
second causes a warning looking something like:

    ------------[ cut here ]------------
    R=00000012: folio 11 is not under writeback
    WARNING: CPU: 34 PID: 654 at fs/netfs/write_collect.c:105
    ...
    CPU: 34 PID: 654 Comm: kworker/u386:27 Tainted: G S ...
    ...
    Workqueue: events_unbound netfs_write_collection_worker
    ...
    RIP: 0010:netfs_writeback_lookup_folio

Fix this by making the flush-and-wait unconditional.  It will do nothing if
there are no folios in the pagecache and will return quickly if there are
no folios in the region specified.

Further, move the WBC attachment above the flush call as the flush is going
to attach a WBC and detach it again if it is not present - and since we
need one anyway we might as well share it.

Fixes: 41d8e7673a77 ("netfs: Implement a write-through caching option")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202404161031.468b84f-oliver.sang@intel.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Eric Van Hensbergen <ericvh@kernel.org>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Christian Schoenebeck <linux_oss@crudebyte.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
cc: v9fs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
---
 fs/netfs/buffered_write.c |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

Comments

Jeff Layton April 26, 2024, 11:43 a.m. UTC | #1
On Fri, 2024-04-26 at 12:15 +0100, David Howells wrote:
> In netfs_perform_write(), when the file is marked NETFS_ICTX_WRITETHROUGH
> or O_*SYNC or RWF_*SYNC was specified, write-through caching is performed
> on a buffered file.  When setting up for write-through, we flush any
> conflicting writes in the region and wait for the write to complete,
> failing if there's a write error to return.
> 
> The issue arises if we're writing at or above the EOF position because we
> skip the flush and - more importantly - the wait.  This becomes a problem
> if there's a partial folio at the end of the file that is being written out
> and we want to make a write to it too.  Both the already-running write and
> the write we start both want to clear the writeback mark, but whoever is
> second causes a warning looking something like:
> 
>     ------------[ cut here ]------------
>     R=00000012: folio 11 is not under writeback
>     WARNING: CPU: 34 PID: 654 at fs/netfs/write_collect.c:105
>     ...
>     CPU: 34 PID: 654 Comm: kworker/u386:27 Tainted: G S ...
>     ...
>     Workqueue: events_unbound netfs_write_collection_worker
>     ...
>     RIP: 0010:netfs_writeback_lookup_folio
> 
> Fix this by making the flush-and-wait unconditional.  It will do nothing if
> there are no folios in the pagecache and will return quickly if there are
> no folios in the region specified.
> 
> Further, move the WBC attachment above the flush call as the flush is going
> to attach a WBC and detach it again if it is not present - and since we
> need one anyway we might as well share it.
> 
> Fixes: 41d8e7673a77 ("netfs: Implement a write-through caching option")
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Closes: https://lore.kernel.org/oe-lkp/202404161031.468b84f-oliver.sang@intel.com
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Eric Van Hensbergen <ericvh@kernel.org>
> cc: Latchesar Ionkov <lucho@ionkov.net>
> cc: Dominique Martinet <asmadeus@codewreck.org>
> cc: Christian Schoenebeck <linux_oss@crudebyte.com>
> cc: Marc Dionne <marc.dionne@auristor.com>
> cc: netfs@lists.linux.dev
> cc: linux-fsdevel@vger.kernel.org
> cc: linux-mm@kvack.org
> cc: v9fs@lists.linux.dev
> cc: linux-afs@lists.infradead.org
> cc: linux-cifs@vger.kernel.org
> ---
>  fs/netfs/buffered_write.c |   13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
> index 9a0d32e4b422..07aff231926c 100644
> --- a/fs/netfs/buffered_write.c
> +++ b/fs/netfs/buffered_write.c
> @@ -172,15 +172,14 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
>  	if (unlikely(test_bit(NETFS_ICTX_WRITETHROUGH, &ctx->flags) ||
>  		     iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC))
>  	    ) {
> -		if (pos < i_size_read(inode)) {
> -			ret = filemap_write_and_wait_range(mapping, pos, pos + iter->count);
> -			if (ret < 0) {
> -				goto out;
> -			}
> -		}
> -
>  		wbc_attach_fdatawrite_inode(&wbc, mapping->host);
>  
> +		ret = filemap_write_and_wait_range(mapping, pos, pos + iter->count);
> +		if (ret < 0) {
> +			wbc_detach_inode(&wbc);
> +			goto out;
> +		}
> +
>  		wreq = netfs_begin_writethrough(iocb, iter->count);
>  		if (IS_ERR(wreq)) {
>  			wbc_detach_inode(&wbc);
> 

Reviewed-by: Jeffrey Layton <jlayton@kernel.org>
diff mbox series

Patch

diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index 9a0d32e4b422..07aff231926c 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -172,15 +172,14 @@  ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 	if (unlikely(test_bit(NETFS_ICTX_WRITETHROUGH, &ctx->flags) ||
 		     iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC))
 	    ) {
-		if (pos < i_size_read(inode)) {
-			ret = filemap_write_and_wait_range(mapping, pos, pos + iter->count);
-			if (ret < 0) {
-				goto out;
-			}
-		}
-
 		wbc_attach_fdatawrite_inode(&wbc, mapping->host);
 
+		ret = filemap_write_and_wait_range(mapping, pos, pos + iter->count);
+		if (ret < 0) {
+			wbc_detach_inode(&wbc);
+			goto out;
+		}
+
 		wreq = netfs_begin_writethrough(iocb, iter->count);
 		if (IS_ERR(wreq)) {
 			wbc_detach_inode(&wbc);