linux-kernel - Re: [PATCH v2] libata: Use per port sync for detach

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Message-ID: <ecd1b0a6-8cdf-1895-a0e8-1bbd98a37887@huawei.com>
Date:   Thu, 21 May 2020 09:16:56 +0100
From:   John Garry <john.garry@...wei.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>, <axboe@...nel.dk>
CC:     "open list:LIBATA SUBSYSTEM (Serial and Parallel ATA drivers)" 
        <linux-ide@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] libata: Use per port sync for detach

On 21/05/2020 05:30, Kai-Heng Feng wrote:
> Commit 130f4caf145c ("libata: Ensure ata_port probe has completed before
> detach") may cause system freeze during suspend.
> 
> Using async_synchronize_full() in PM callbacks is wrong, since async
> callbacks that are already scheduled may wait for not-yet-scheduled
> callbacks, causes a circular dependency.
> 
> Instead of using big hammer like async_synchronize_full(), use async
> cookie to make sure port probe are synced, without affecting other
> scheduled PM callbacks.
> 

Apart from nit, it looks ok.

Cheers,
John

> Fixes: 130f4caf145c ("libata: Ensure ata_port probe has completed before detach")
> BugLink: https://bugs.launchpad.net/bugs/1867983
> Suggested-by: John Garry <john.garry@...wei.com>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
> v2:
>   - Sync up to cookie + 1.
>   - Squash the synchronization into the same loop.
> 
>   drivers/ata/libata-core.c | 9 ++++-----
>   include/linux/libata.h    | 3 +++
>   2 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index beca5f91bb4c..b6be84f2cecb 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -42,7 +42,6 @@
>   #include <linux/workqueue.h>
>   #include <linux/scatterlist.h>
>   #include <linux/io.h>
> -#include <linux/async.h>
>   #include <linux/log2.h>
>   #include <linux/slab.h>
>   #include <linux/glob.h>
> @@ -5778,7 +5777,7 @@ int ata_host_register(struct ata_host *host, struct scsi_host_template *sht)
>   	/* perform each probe asynchronously */
>   	for (i = 0; i < host->n_ports; i++) {
>   		struct ata_port *ap = host->ports[i];
> -		async_schedule(async_port_probe, ap);
> +		ap->cookie = async_schedule(async_port_probe, ap);
>   	}
>   
>   	return 0;
> @@ -5921,10 +5920,10 @@ void ata_host_detach(struct ata_host *host)
>   	int i;
>   
>   	/* Ensure ata_port probe has completed */

nit: maybe we can relocate this comment

> -	async_synchronize_full();
> -
> -	for (i = 0; i < host->n_ports; i++)
> +	for (i = 0; i < host->n_ports; i++) {
> +		async_synchronize_cookie(host->ports[i]->cookie + 1);
>   		ata_port_detach(host->ports[i]);
> +	}
>   
>   	/* the host is dead now, dissociate ACPI */
>   	ata_acpi_dissociate(host);
> diff --git a/include/linux/libata.h b/include/linux/libata.h
> index cffa4714bfa8..ae6dfc107ea8 100644
> --- a/include/linux/libata.h
> +++ b/include/linux/libata.h
> @@ -22,6 +22,7 @@
>   #include <linux/acpi.h>
>   #include <linux/cdrom.h>
>   #include <linux/sched.h>
> +#include <linux/async.h>
>   
>   /*
>    * Define if arch has non-standard setup.  This is a _PCI_ standard
> @@ -872,6 +873,8 @@ struct ata_port {
>   	struct timer_list	fastdrain_timer;
>   	unsigned long		fastdrain_cnt;
>   
> +	async_cookie_t		cookie;
> +
>   	int			em_message_type;
>   	void			*private_data;
>   
>