linux-kernel - Re: [PATCH] scsi: target: iscsi: cxgbit: fix sleep-in-atomic-context bug in cxgbit_abort

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Message-ID: <2c8985b8.107370.1839e591d73.Coremail.duoming@zju.edu.cn>
Date:   Mon, 3 Oct 2022 22:56:23 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     "Dmitry Bogdanov" <d.bogdanov@...ro.com>
Cc:     linux-kernel@...r.kernel.org, martin.petersen@...cle.com,
        kuba@...nel.org, davem@...emloft.net, andrii@...nel.org,
        gregkh@...uxfoundation.org, linux-scsi@...r.kernel.org,
        target-devel@...r.kernel.org
Subject: Re: [PATCH] scsi: target: iscsi: cxgbit: fix
 sleep-in-atomic-context bug in cxgbit_abort_conn

Hello,

On Mon, 3 Oct 2022 17:46:02 +0300 Dmitry Bogdanov wrote:

> On Sun, Oct 02, 2022 at 09:40:47AM +0800, Duoming Zhou wrote:
> > 
> > The function iscsit_handle_time2retain_timeout() is a timer handler that
> > runs in an atomic context, but it calls "alloc_skb(0, GFP_KERNEL | ...)"
> > that may sleep. As a result, the sleep-in-atomic-context bug will happen.
> > The process is shown below:
> > 
> > iscsit_handle_time2retain_timeout()
> >  iscsit_close_session()
> >   iscsit_free_connection_recovery_entries()
> >    iscsit_free_cmd()
> >     __iscsit_free_cmd()
> >      cxgbit_unmap_cmd()
> >       cxgbit_abort_conn()
> >        alloc_skb(0, GFP_KERNEL | ...) //may sleep
> > 
> > This patch changes the gfp_t parameter of alloc_skb() from GFP_KERNEL to
> > GFP_ATOMIC in order to mitigate the bug.
> > 
> > Fixes: 1ae01724ae92 ("cxgbit: Abort the TCP connection in case of data out timeout")
> > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> > ---
> >  drivers/target/iscsi/cxgbit/cxgbit_cm.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/target/iscsi/cxgbit/cxgbit_cm.c b/drivers/target/iscsi/cxgbit/cxgbit_cm.c
> > index 3336d2b78bf..eb3da6d2c62 100644
> > --- a/drivers/target/iscsi/cxgbit/cxgbit_cm.c
> > +++ b/drivers/target/iscsi/cxgbit/cxgbit_cm.c
> > @@ -697,7 +697,7 @@ __cxgbit_abort_conn(struct cxgbit_sock *csk, struct sk_buff *skb)
> > 
> >  void cxgbit_abort_conn(struct cxgbit_sock *csk)
> >  {
> > -       struct sk_buff *skb = alloc_skb(0, GFP_KERNEL | __GFP_NOFAIL);
> > +       struct sk_buff *skb = alloc_skb(0, GFP_ATOMIC | __GFP_NOFAIL);
> > 
> >         cxgbit_get_csk(csk);
> >         cxgbit_init_wr_wait(&csk->com.wr_wait);
> > --
> > 2.17.1
> >
> 
> The last line in cxgbit_abort_conn is cxgbit_wait_for_reply() which
> also should not be called in interrupt context.

I agree with you.

> Anyway this issue is not due to cxgbit, it is common for iSCSI itself:
> iscsit_close_session()
>   iscsit_free_connection_recovery_entries()
>     iscsit_free_cmd()
>       transport_generic_free_cmd()
>         target_wait_free_cmd()
>           wait_for_completion_timeout()

I understand.

> IMHO, there is no reason to call iscsit_close_session in an atomic context.
> I have two patches relaited Time2Retain timer. I will share them today.

That's great, thank you!

Best regards,
Duoming Zhou