linux-kernel - Re: io_uring: BUG: kernel NULL pointer dereference

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Date:   Mon, 25 May 2020 17:11:37 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Stefano Garzarella <sgarzare@...hat.com>,
        Jens Axboe <axboe@...nel.dk>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: io_uring: BUG: kernel NULL pointer dereference

On 25/05/2020 16:45, Stefano Garzarella wrote:
> On Mon, May 25, 2020 at 12:30:51PM +0200, Stefano Garzarella wrote:
>>
>> I'll try to bisect, but I have some suspicions about:
>> b41e98524e42 io_uring: add per-task callback handler
> 
> I confirm, the bisection ended with this:
> b41e98524e424d104aa7851d54fd65820759875a is the first bad commit
> 
> I'll try to figure out what happened.

Hmm, I'd start with temporary un-union req->task_work.
Could you give it a try?


diff --git a/fs/io_uring.c b/fs/io_uring.c
index e173cea621de..cfab79254d0a 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -645,7 +645,7 @@ struct io_kiocb {

 	struct percpu_ref	*fixed_file_refs;

-	union {
+	// union {
 		/*
 		 * Only commands that never go async can use the below fields,
 		 * obviously. Right now only IORING_OP_POLL_ADD uses them, and
@@ -658,7 +658,7 @@ struct io_kiocb {
 			struct async_poll	*apoll;
 		};
 		struct io_wq_work	work;
-	};
+	// };
 };

 #define IO_PLUG_THRESHOLD		2


-- 
Pavel Begunkov