This makes sense to me. I was hoping Chris would comment since he's looked
more closely at the locks. @chris ?
On Monday, July 2, 2018 at 8:00:48 AM UTC-7, Anoob Soman wrote:
>
> When a target sends Check Condition, whilst initiator is busy xmiting
> re-queued data, could lead to race between iscsi_complete_task() and
> iscsi_xmit_task() and eventually crashing with the following kernel
> backtrace.
>
> [3326150.987523] ALERT: BUG: unable to handle kernel NULL pointer
> dereference at 0000000000000078
> [3326150.987549] ALERT: IP: [<ffffffffa05ce70d>] iscsi_xmit_task+0x2d/0xc0
> [libiscsi]
> [3326150.987571] WARN: PGD 569c8067 PUD 569c9067 PMD 0
> [3326150.987582] WARN: Oops: 0002 [#1] SMP
> [3326150.987593] WARN: Modules linked in: tun nfsv3 nfs fscache
> dm_round_robin
> [3326150.987762] WARN: CPU: 2 PID: 8399 Comm: kworker/u32:1 Tainted: G O
> 4.4.0+2 #1
> [3326150.987774] WARN: Hardware name: Dell Inc. PowerEdge R720/0W7JN5,
> BIOS 2.5.4 01/22/2016
> [3326150.987790] WARN: Workqueue: iscsi_q_13 iscsi_xmitworker [libiscsi]
> [3326150.987799] WARN: task: ffff8801d50f3800 ti: ffff8801f5458000
> task.ti: ffff8801f5458000
> [3326150.987810] WARN: RIP: e030:[<ffffffffa05ce70d>] [<ffffffffa05ce70d>]
> iscsi_xmit_task+0x2d/0xc0 [libiscsi]
> [3326150.987825] WARN: RSP: e02b:ffff8801f545bdb0 EFLAGS: 00010246
> [3326150.987831] WARN: RAX: 00000000ffffffc3 RBX: ffff880282d2ab20 RCX:
> ffff88026b6ac480
> [3326150.987842] WARN: RDX: 0000000000000000 RSI: 00000000fffffe01 RDI:
> ffff880282d2ab20
> [3326150.987852] WARN: RBP: ffff8801f545bdc8 R08: 0000000000000000 R09:
> 0000000000000008
> [3326150.987862] WARN: R10: 0000000000000000 R11: 000000000000fe88 R12:
> 0000000000000000
> [3326150.987872] WARN: R13: ffff880282d2abe8 R14: ffff880282d2abd8 R15:
> ffff880282d2ac08
> [3326150.987890] WARN: FS: 00007f5a866b4840(0000)
> GS:ffff88028a640000(0000) knlGS:0000000000000000
> [3326150.987900] WARN: CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033
> [3326150.987907] WARN: CR2: 0000000000000078 CR3: 0000000070244000 CR4:
> 0000000000042660
> [3326150.987918] WARN: Stack:
> [3326150.987924] WARN: ffff880282d2ad58 ffff880282d2ab20 ffff880282d2abe8
> ffff8801f545be18
> [3326150.987938] WARN: ffffffffa05cea90 ffff880282d2abf8 ffff88026b59cc80
> ffff88026b59cc00
> [3326150.987951] WARN: ffff88022acf32c0 ffff880289491800 ffff880255a80800
> 0000000000000400
> [3326150.987964] WARN: Call Trace:
> [3326150.987975] WARN: [<ffffffffa05cea90>] iscsi_xmitworker+0x2f0/0x360
> [libiscsi]
> [3326150.987988] WARN: [<ffffffff8108862c>] process_one_work+0x1fc/0x3b0
> [3326150.987997] WARN: [<ffffffff81088f95>] worker_thread+0x2a5/0x470
> [3326150.988006] WARN: [<ffffffff8159cad8>] ? __schedule+0x648/0x870
> [3326150.988015] WARN: [<ffffffff81088cf0>] ? rescuer_thread+0x300/0x300
> [3326150.988023] WARN: [<ffffffff8108ddf5>] kthread+0xd5/0xe0
> [3326150.988031] WARN: [<ffffffff8108dd20>] ? kthread_stop+0x110/0x110
> [3326150.988040] WARN: [<ffffffff815a0bcf>] ret_from_fork+0x3f/0x70
> [3326150.988048] WARN: [<ffffffff8108dd20>] ? kthread_stop+0x110/0x110
> [3326150.988127] ALERT: RIP [<ffffffffa05ce70d>] iscsi_xmit_task+0x2d/0xc0
> [libiscsi]
> [3326150.988138] WARN: RSP <ffff8801f545bdb0>
> [3326150.988144] WARN: CR2: 0000000000000078
> [3326151.020366] WARN: ---[ end trace 1c60974d4678d81b ]---
>
> Commit 6f8830f5bbab (scsi: libiscsi: add lock around task lists to fix
> list
> corruption regression) introduced "taskqueuelock" to fix list corruption
> during
> the race, but this wasn't enough.
>
> Re-setting of conn->task to NULL, could race with iscsi_xmit_task().
> iscsi_complete_task()
> {
> ....
> if (conn->task == task)
> conn->task = NULL;
> }
>
> conn->task in iscsi_xmit_task() could be NULL and so will be task.
> __iscsi_get_task(task) will crash (NullPtr de-ref), trying to access
> refcount.
>
> iscsi_xmit_task()
> {
> struct iscsi_task *task = conn->task;
>
> __iscsi_get_task(task);
> }
>
> This commit will take extra conn->session->back_lock in iscsi_xmit_task()
> to ensure iscsi_xmit_task() waits for iscsi_complete_task(), if
> iscsi_complete_task() wins the race.
> If iscsi_xmit_task() wins the race, iscsi_xmit_task() increments
> task->refcount
> (__iscsi_get_task) ensuring iscsi_complete_task() will not
> iscsi_free_task().
>
> Signed-off-by: Anoob Soman <anoob.so...@citrix.com>
> ---
> drivers/scsi/libiscsi.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
> index d609383..aa3be6f 100644
> --- a/drivers/scsi/libiscsi.c
> +++ b/drivers/scsi/libiscsi.c
> @@ -1449,7 +1449,13 @@ static int iscsi_xmit_task(struct iscsi_conn *conn)
> if (test_bit(ISCSI_SUSPEND_BIT, &conn->suspend_tx))
> return -ENODATA;
>
> + spin_lock_bh(&conn->session->back_lock);
> + if (conn->task == NULL) {
> + spin_unlock_bh(&conn->session->back_lock);
> + return -ENODATA;
> + }
> __iscsi_get_task(task);
> + spin_unlock_bh(&conn->session->back_lock);
> spin_unlock_bh(&conn->session->frwd_lock);
> rc = conn->session->tt->xmit_task(task);
> spin_lock_bh(&conn->session->frwd_lock);
> --
> 1.8.3.1
>
>
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