linux-kernel - Re: Slab corruption in floppy driver module

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Date:	Tue, 24 Jan 2012 17:31:53 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Suresh Jayaraman <sjayaraman@...e.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: Slab corruption in floppy driver module

On Tue, Jan 24, 2012 at 06:49:37PM +0530, Suresh Jayaraman wrote:

[..]

> [   33.372026]  ffff88041dd9be08 ffffffff8134f517 ffff88041dd9be28
> ffff88041da9bc68
> [   33.372026] Call Trace:
> [   33.372026]  [<ffffffff81243a15>] blk_put_queue+0x15/0x20
> [   33.372026]  [<ffffffff8124d4ff>] disk_release+0x8f/0xd0
> [   33.372026]  [<ffffffff8134f517>] device_release+0x27/0xa0
> [   33.372026]  [<ffffffff812754fd>] kobject_cleanup+0x6d/0x1b0
> [   33.372026]  [<ffffffff8127564d>] kobject_release+0xd/0x10
> [   33.372026]  [<ffffffff81276b17>] kref_put+0x37/0x70
> [   33.372026]  [<ffffffff81275387>] kobject_put+0x27/0x60
> [   33.372026]  [<ffffffff8124dbf7>] put_disk+0x17/0x20
> [   33.372026]  [<ffffffffa00fa92c>] floppy_init+0x1c1/0x675 [floppy]
> [   33.372026]  [<ffffffffa00fae37>] floppy_module_init+0x57/0x220 [floppy]
> [   33.372026]  [<ffffffff810001d3>] do_one_initcall+0x43/0x180
> [   33.372026]  [<ffffffff810a526d>] sys_init_module+0xcd/0x240
> [   33.372026]  [<ffffffff8148d4c2>] system_call_fastpath+0x16/0x1b
> [   33.372026]  [<00007f86dce3406a>] 0x7f86dce34069
> [   33.372026] Code: eb cc 48 89 fe 31 c0 48 c7 c7 60 aa 7a 81 e8 26 c4 20 00
> e8 92 c1 20 00 eb 8e 55 48 89 e5 53 48 89 fb 48 83 ec 08 48 85 ff 74 16 <f6> 47
> 3c 01 74 19 48 8d 7b 38 48 c7 c6 40 56 27 81 e8 59 17 00
> [   33.372026] RIP  [<ffffffff81275371>] kobject_put+0x11/0x60
> [   33.372026]  RSP <ffff88041dd9bda8>
> [   33.372026] CR2: ffff88041d986c9c
> [   33.372026] ---[ end trace f624c17dc6e4672a ]---
> --- cut-here ---
> 
> What seems to be happening is after commit f992ae80, add_disk takes a
> extra reference to the queue which is supposed to be put in disk_release().
> In floppy_init() when there were "no floppy controllers found" the control
> goes to out_flush_work. Note that add_disk() is not being called at all and
> so extra reference not taken. We try to put_disk() and the call sequence is
>   put_disk()
>    kobject_put()
>     kref_put()
>      kobject_release()
>       kobject_cleanup()
>        device_release()
>         disk_release()
>          blk_put_queue()  <-- put without a get
>           kobject_put()
> 
> 
> Reverting f992ae80 makes the oops and the slab corruption messages disappear.
> The "no floppy controllers found" message was found in the dmesg.

I am wondering if extra queue reference for gendisk should be taken by driver
and not by add_disk(). Why? Because disk->queue association is setup by
driver and not by add_disk(). That way even if we don't call, add_disk(),
we should be fine.

Thanks
Vivek
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