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Subject: Re: Kernel crashes after 529262d56dbe "block: remove ->poll_fn"
To:     Kirill Tkhai <ktkhai@virtuozzo.com>, hch@lst.de, sagi@grimberg.me,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
References: <0bd2d36e-bef0-b836-7039-124ae4d346a6@virtuozzo.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <c374e085-a86b-6df3-2142-74968f067bc7@kernel.dk>
Date:   Wed, 5 Dec 2018 05:45:15 -0700
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On 12/5/18 5:19 AM, Kirill Tkhai wrote:
> Hi,
> 
> commit 529262d56dbe from today linux-next makes my kernel crash:
> 
> Author: Christoph Hellwig <hch@lst.de>
> Date:   Sun Dec 2 17:46:26 2018 +0100
> 
>     block: remove ->poll_fn
> 
> Traceback is below, config and reproducer (not minimal, just a random one populating swap) are attached.
> 
> [   29.097612] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
> [   29.098730] #PF error: [INSTR]
> [   29.099104] PGD 0 P4D 0 
> [   29.099425] Oops: 0010 [#1] PREEMPT SMP
> [   29.099879] CPU: 3 PID: 925 Comm: bash Not tainted 4.20.0-rc5-next-20181205+ #244
> [   29.100658] RIP: 0010:          (null)
> [   29.101100] Code: Bad RIP value.
> [   29.101480] RSP: 0000:ffffc9000023fb80 EFLAGS: 00010202
> [   29.102061] RAX: ffffffff8182d0e0 RBX: ffff88807ceee000 RCX: 0000000000000000
> [   29.102818] RDX: ffff88807d560f40 RSI: 0000000000000000 RDI: ffff88807ceee000
> [   29.103661] RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000002000
> [   29.104560] R10: 00000000ffffffff R11: ffff88807c854150 R12: 0000000000000000
> [   29.105458] R13: 0000000000000002 R14: ffff88807d7236c0 R15: ffffc9000023fe20
> [   29.106438] FS:  00007faba91d7740(0000) GS:ffff88807db80000(0000) knlGS:0000000000000000
> [   29.107304] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   29.107917] CR2: ffffffffffffffd6 CR3: 000000007a172000 CR4: 00000000000006a0
> [   29.109401] Call Trace:
> [   29.110017]  ? blk_poll+0x27c/0x340
> [   29.110691]  ? submit_bio+0x40/0x120
> [   29.111278]  ? swap_readpage+0x148/0x190
> [   29.111924]  ? read_swap_cache_async+0x53/0x60
> [   29.112670]  ? swap_cluster_readahead+0x231/0x2b0
> [   29.113310]  ? swapin_readahead+0x2ce/0x400
> [   29.113878]  ? pagecache_get_page+0x2b/0x210
> [   29.114416]  ? do_swap_page+0x42c/0x800
> [   29.114919]  ? __handle_mm_fault+0x544/0xdd0
> [   29.115455]  ? handle_mm_fault+0x112/0x230
> [   29.115978]  ? __do_page_fault+0x196/0x410
> [   29.116501]  ? __put_user_4+0x19/0x20
> [   29.116990]  ? page_fault+0x5/0x20
> [   29.117451]  ? page_fault+0x1b/0x20
> [   29.117925] CR2: 0000000000000000
> [   29.118472] ---[ end trace 0faa4ddc190b41fa ]---

Can you try this? The swap read-in poll attempts looks totally
incorrect.


diff --git a/mm/page_io.c b/mm/page_io.c
index 5bdfd21c1bd9..f3455f9f8dc7 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -401,6 +401,8 @@ int swap_readpage(struct page *page, bool synchronous)
 	get_task_struct(current);
 	bio->bi_private = current;
 	bio_set_op_attrs(bio, REQ_OP_READ, 0);
+	if (synchronous)
+		bio->bi_opf |= REQ_HIPRI;
 	count_vm_event(PSWPIN);
 	bio_get(bio);
 	qc = submit_bio(bio);
@@ -411,7 +413,7 @@ int swap_readpage(struct page *page, bool synchronous)
 			break;
 
 		if (!blk_poll(disk->queue, qc, true))
-			break;
+			io_schedule();
 	}
 	__set_current_state(TASK_RUNNING);
 	bio_put(bio);

-- 
Jens Axboe