[Ocfs2-devel] [PATCH] ocfs2: don't use iocb when EIOCBQUEUED returns

[Changwei Ge]

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.
>From 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]
? ocfs2_check_range_for_refcount+0x150/0x150 [ocfs2]
aio_run_iocb+0x229/0x2f0
? try_to_wake_up+0x380/0x380
do_io_submit+0x291/0x540
? syscall_trace_leave+0xad/0x130
SyS_io_submit+0x10/0x20
system_call_fastpath+0x16/0x75

Signed-off-by: Changwei Ge <ge.changwei at h3c.com>
---
 fs/ocfs2/file.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index 5d1784a..1393ff2 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2343,7 +2343,7 @@ static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
 
 	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
@@ -2463,7 +2463,7 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
 	trace_generic_file_aio_read_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)) {
-- 
2.7.4