[PATCH] kernfs: handle poll correctly on 'direct_read' files.

[NeilBrown]

Kernfs supports two styles of read: direct_read and seqfile_read.

The latter supports 'poll' correctly thanks to the update of
'->event' in kernfs_seq_show.
The former does not as '->event' is never updated on a read.

So add an appropriate update in kernfs_file_direct_read().

This was noticed because some 'md' sysfs attributes were
recently changed to use direct reads.

Reported-by: Prakash Punnoor <prak...@punnoor.de>
Reported-by: Torsten Kaiser <just.for.l...@googlemail.com>
Fixes: 750f199ee8b578062341e6ddfe36c59ac8ff2dcb
Signed-off-by: NeilBrown <ne...@suse.de>

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index b684e8a132e6..2bacb9988566 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -207,6 +207,7 @@ static ssize_t kernfs_file_direct_read(struct 
kernfs_open_file *of,
                goto out_free;
        }
 
+       of->event = atomic_read(&of->kn->attr.open->event);
        ops = kernfs_ops(of->kn);
        if (ops->read)
                len = ops->read(of, buf, len, *ppos);

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