mpage: terminate read-ahead on read error

For exFAT filesystems with 4MB read_ahead_size, removing the storage
device during read operations can delay EIO error reporting by several
minutes.  This occurs because the read-ahead implementation in mpage
doesn't handle errors.

Another reason for the delay is that the filesystem requires metadata to
issue file read request.  When the storage device is removed, the metadata
buffers are invalidated, causing mpage to repeatedly attempt to fetch
metadata during each get_block call.

The original purpose of this patch is terminate read ahead when we fail to
get metadata, to make the patch more generic, implement it by checking
folio status, instead of checking the return of get_block().

So, if a folio is synchronously unlocked and non-uptodate, should we quit
the read ahead?

I think it depends on whether the error is permanent or temporary, and
whether further read ahead might succeed.  A device being unplugged is one
reason for returning such a folio, but we could return it for many other
reasons (e.g., metadata errors).  I think most errors won't be restored in
a short time, so we should quit read ahead when they occur.

Link: https://lkml.kernel.org/r/20250829023659.688649-1-chizhiling@163.com


Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Sungjong Seo <sj1557.seo@samsung.com>
Cc: Yuezhang Mo <Yuezhang.Mo@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>