6.8-stable review patch. If anyone has any objections, please let me know.
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From: David Howells dhowells@redhat.com
[ Upstream commit c97f59e276d4e93480f29a70accbd0d7273cf3f5 ]
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 Link: https://lore.kernel.org/r/2150448.1714130115@warthog.procyon.org.uk Reviewed-by: Jeffrey Layton jlayton@kernel.org 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 Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Sasha Levin sashal@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 8f13ca8fbc74d..267b622d923b1 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);