linux-kernel - Re: [PATCH] IB/iser: Protect tasks cleanup in case iser connection was stopped

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Date:   Wed, 5 Jul 2023 09:22:08 +0000
From:   Rock Li(李宏伟) <lihongweizz@...pur.com>
To:     "leon@...nel.org" <leon@...nel.org>
CC:     "sagi@...mberg.me" <sagi@...mberg.me>,
        "mgurtovoy@...dia.com" <mgurtovoy@...dia.com>,
        "jgg@...pe.ca" <jgg@...pe.ca>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] IB/iser: Protect tasks cleanup in case iser connection
 was stopped

> > On Tue, Jul 04, 2023 at 08:51:44AM +0800, lihongweizz wrote:
> > From: Rock Li <lihongweizz@...pur.com>
> >
> > We met a crash issue as below:
> > ...
> >  #7 [ff61b991f6f63d10] page_fault at ffffffffab80111e
> >     [exception RIP: iscsi_iser_cleanup_task+13]
> >     RIP: ffffffffc046c04d RSP: ff61b991f6f63dc0 RFLAGS: 00010246
> >     RAX: 0000000000000000 RBX: ff4bd0aalf7a5610 RCX: ff61b991f6f63dc8
> >     RDX: ff61b991f6f63d68 RSI: ff61b991f6f63d58 RDI: ff4bd0aalf6cdc00
> >     RBP: 0000000000000005 R8: 0000000000000073 R9:
> 0000000000000005
> >     R10: 0000000000000000 R11: 00000ccde3e0f5c0 R12:
> ff4bd08c0e0631f8
> >     R13: ff4bd0a95ffd3c78 R14: ff4bd0a95ffd3c78 R15: ff4bd0aalf6cdc00
> >     ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
> >  #8 [ff616991f6f63dc0] __iscsi_put_task at ffffffffc0bd3652 [libiscsi]
> >  #9 [ff61b991f6f63e00] iscsi_put_task at ffffffffc0bd36e9 [libiscsi]
> > ...
> >
> > After analysing the vmcore, we find that the iser connection was
> > already stopped before abort handler running. The iser_conn is already
> > unbindded and released. So we add iser connection validation check
> > inside cleanup task to fix this corner case.
> >
> > Signed-off-by: Rock Li <lihongweizz@...pur.com>
> > ---
> >  drivers/infiniband/ulp/iser/iscsi_iser.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/infiniband/ulp/iser/iscsi_iser.c
> > b/drivers/infiniband/ulp/iser/iscsi_iser.c
> > index bb9aaff92ca3..35dfbf41fc40 100644
> > --- a/drivers/infiniband/ulp/iser/iscsi_iser.c
> > +++ b/drivers/infiniband/ulp/iser/iscsi_iser.c
> > @@ -366,7 +366,12 @@ static void iscsi_iser_cleanup_task(struct
iscsi_task
> *task)
> >  	struct iscsi_iser_task *iser_task = task->dd_data;
> >  	struct iser_tx_desc *tx_desc = &iser_task->desc;
> >  	struct iser_conn *iser_conn = task->conn->dd_data;
> > -	struct iser_device *device = iser_conn->ib_conn.device;
> > +	struct iser_device *device;
> > +
> > +	/* stop connection might happens before iser cleanup work */
> > +	if (!iser_conn)
> > +		return;
> 
> And what prevents from iser_conn being not valid here?
> For example, in the flow:
> 1. Start iscsi_iser_cleanup_task
> 2. Get valid task->conn->dd_data
> 3. Pass this if (..) check
> 4. Context switch and release connection 5. iser_conn now points to
released
> memory.
> 
> Thanks

Hi Leon,
Thanks for your reply:) In case iscsi_stop_conn was executed cocurrently or
after iscsi_iser_cleanup_task, above issue would happen.
I've confirmed the values in iscsi_cls_conn and iscsi_conn instances from
vmcore:

iscsi_stop_conn
  ...
  WRITE_ONCE(conn->state, ISCSI_CONN_FAILED);      --- confirmed
  ...
  conn->transport->stop_conn => iscsi_iser_conn_stop
    iscsi_conn_stop
      ...
      conn->c_stage = ISCSI_CONN_STOPPED;          --- confirmed
    conn->dd_data = NULL;                          --- confirmed

The crash scene tells us that iscsi_stop_conn was executed before
iscsi_iser_cleanup_task start, the iser_conn instance was already released. 

> 
> > +	device = iser_conn->ib_conn.device;
> >
> >  	/* DEVICE_REMOVAL event might have already released the device */
> >  	if (!device)
> > --
> > 2.27.0
> >

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