[PATCH] scsi: target: iscsi: cxgbit: fix sleep-in-atomic-context bug in cxgbit_abort_conn

[PATCH] scsi: target: iscsi: cxgbit: fix sleep-in-atomic-context bug in cxgbit_abort_conn

[Duoming Zhou]

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@zju.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

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

[Dmitry Bogdanov]

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@zju.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.

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()

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.

BR,
 Dmitry 

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

[duoming]

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@zju.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