linux-kernel - Re: ata: BUG in ata_sff_hsm

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Message-ID: <CACT4Y+Zf4PwWS3ACCAtfnrwGnN3DKc_yYXWcJayLjBnB8f_JVQ@mail.gmail.com>
Date:	Mon, 1 Feb 2016 11:46:21 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	syzkaller <syzkaller@...glegroups.com>, linux-ide@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jeff Garzik <jgarzik@...hat.com>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: ata: BUG in ata_sff_hsm_move

On Fri, Jan 29, 2016 at 9:23 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Fri, Jan 29, 2016 at 02:40:33PM +0100, Dmitry Vyukov wrote:
>> It now deadlocks at this stack. It is probably not OK to call
>> ata_sff_hsm_move holding the spinlock.
>
> Yeah, the locking is pretty messed up with the polling path.  Can you
> please try the following?


No crashes over the weekend. We can consider this fixed.
Thanks!



> diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
> index cdf6215..7dbba38 100644
> --- a/drivers/ata/libata-sff.c
> +++ b/drivers/ata/libata-sff.c
> @@ -997,12 +997,9 @@ static inline int ata_hsm_ok_in_wq(struct ata_port *ap,
>  static void ata_hsm_qc_complete(struct ata_queued_cmd *qc, int in_wq)
>  {
>         struct ata_port *ap = qc->ap;
> -       unsigned long flags;
>
>         if (ap->ops->error_handler) {
>                 if (in_wq) {
> -                       spin_lock_irqsave(ap->lock, flags);
> -
>                         /* EH might have kicked in while host lock is
>                          * released.
>                          */
> @@ -1014,8 +1011,6 @@ static void ata_hsm_qc_complete(struct ata_queued_cmd *qc, int in_wq)
>                                 } else
>                                         ata_port_freeze(ap);
>                         }
> -
> -                       spin_unlock_irqrestore(ap->lock, flags);
>                 } else {
>                         if (likely(!(qc->err_mask & AC_ERR_HSM)))
>                                 ata_qc_complete(qc);
> @@ -1024,10 +1019,8 @@ static void ata_hsm_qc_complete(struct ata_queued_cmd *qc, int in_wq)
>                 }
>         } else {
>                 if (in_wq) {
> -                       spin_lock_irqsave(ap->lock, flags);
>                         ata_sff_irq_on(ap);
>                         ata_qc_complete(qc);
> -                       spin_unlock_irqrestore(ap->lock, flags);
>                 } else
>                         ata_qc_complete(qc);
>         }
> @@ -1048,9 +1041,10 @@ int ata_sff_hsm_move(struct ata_port *ap, struct ata_queued_cmd *qc,
>  {
>         struct ata_link *link = qc->dev->link;
>         struct ata_eh_info *ehi = &link->eh_info;
> -       unsigned long flags = 0;
>         int poll_next;
>
> +       lockdep_assert_held(ap->lock);
> +
>         WARN_ON_ONCE((qc->flags & ATA_QCFLAG_ACTIVE) == 0);
>
>         /* Make sure ata_sff_qc_issue() does not throw things
> @@ -1112,14 +1106,6 @@ int ata_sff_hsm_move(struct ata_port *ap, struct ata_queued_cmd *qc,
>                         }
>                 }
>
> -               /* Send the CDB (atapi) or the first data block (ata pio out).
> -                * During the state transition, interrupt handler shouldn't
> -                * be invoked before the data transfer is complete and
> -                * hsm_task_state is changed. Hence, the following locking.
> -                */
> -               if (in_wq)
> -                       spin_lock_irqsave(ap->lock, flags);
> -
>                 if (qc->tf.protocol == ATA_PROT_PIO) {
>                         /* PIO data out protocol.
>                          * send first data block.
> @@ -1135,9 +1121,6 @@ int ata_sff_hsm_move(struct ata_port *ap, struct ata_queued_cmd *qc,
>                         /* send CDB */
>                         atapi_send_cdb(ap, qc);
>
> -               if (in_wq)
> -                       spin_unlock_irqrestore(ap->lock, flags);
> -
>                 /* if polling, ata_sff_pio_task() handles the rest.
>                  * otherwise, interrupt handler takes over from here.
>                  */
> @@ -1361,12 +1344,14 @@ static void ata_sff_pio_task(struct work_struct *work)
>         u8 status;
>         int poll_next;
>
> +       spin_lock_irq(ap->lock);
> +
>         BUG_ON(ap->sff_pio_task_link == NULL);
>         /* qc can be NULL if timeout occurred */
>         qc = ata_qc_from_tag(ap, link->active_tag);
>         if (!qc) {
>                 ap->sff_pio_task_link = NULL;
> -               return;
> +               goto out_unlock;
>         }
>
>  fsm_start:
> @@ -1381,11 +1366,14 @@ static void ata_sff_pio_task(struct work_struct *work)
>          */
>         status = ata_sff_busy_wait(ap, ATA_BUSY, 5);
>         if (status & ATA_BUSY) {
> +               spin_unlock_irq(ap->lock);
>                 ata_msleep(ap, 2);
> +               spin_lock_irq(ap->lock);
> +
>                 status = ata_sff_busy_wait(ap, ATA_BUSY, 10);
>                 if (status & ATA_BUSY) {
>                         ata_sff_queue_pio_task(link, ATA_SHORT_PAUSE);
> -                       return;
> +                       goto out_unlock;
>                 }
>         }
>
> @@ -1402,6 +1390,8 @@ static void ata_sff_pio_task(struct work_struct *work)
>          */
>         if (poll_next)
>                 goto fsm_start;
> +out_unlock:
> +       spin_unlock_irq(ap->lock);
>  }
>
>  /**