ocfs2: don't use iocb when EIOCBQUEUED returns

When -EIOCBQUEUED returns, it means that aio_complete() will be called
from dio_complete(), which is an asynchronous progress against
write_iter. Generally, IO is a very slow progress than executing
instruction, but we still can't take the risk to access a freed iocb.

And we do face a BUG crash issue. Using the crash tool, iocb is
obviously freed already.

crash> struct -x kiocb ffff881a350f5900
struct kiocb {
ki_filp = 0xffff881a350f5a80,
ki_pos = 0x0,
ki_complete = 0x0,
private = 0x0,
ki_flags = 0x0
}

And the backtrace shows:
ocfs2_file_write_iter+0xcaa/0xd00 [ocfs2]
aio_run_iocb+0x229/0x2f0
do_io_submit+0x291/0x540
SyS_io_submit+0x10/0x20
system_call_fastpath+0x16/0x75

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Changwei Ge <[e-mail]>
Reviewed-by: Andrew Morton <[e-mail]>
Cc: Mark Fasheh <[e-mail]>
Cc: Joel Becker <[e-mail]>
Cc: Junxiao Bi <[e-mail]>
Cc: Joseph Qi <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/ocfs2/file.c

···
 
 	written = __generic_file_write_iter(iocb, from);
 	/* buffered aio wouldn't have proper lock coverage today */
-	BUG_ON(written == -EIOCBQUEUED && !(iocb->ki_flags & IOCB_DIRECT));
+	BUG_ON(written == -EIOCBQUEUED && !direct_io);
 
 	/*
 	 * deep in g_f_a_w_n()->ocfs2_direct_IO we pass in a ocfs2_dio_end_io
···
 	trace_generic_file_read_iter_ret(ret);
 
 	/* buffered aio wouldn't have proper lock coverage today */
-	BUG_ON(ret == -EIOCBQUEUED && !(iocb->ki_flags & IOCB_DIRECT));
+	BUG_ON(ret == -EIOCBQUEUED && !direct_io);
 
 	/* see ocfs2_file_write_iter */
 	if (ret == -EIOCBQUEUED || !ocfs2_iocb_is_rw_locked(iocb)) {