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Subject: Re: [PATCH v3] libata: Use per port sync for detach
From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
In-Reply-To: <b13888c3-d1f9-7e6e-d25e-0287b3d7ba9b@huawei.com>
Date:   Thu, 18 Jun 2020 13:43:16 +0800
Cc:     Jens Axboe <axboe@kernel.dk>,
        "open list:LIBATA SUBSYSTEM (Serial and Parallel ATA drivers)" 
        <linux-ide@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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Message-Id: <EEE4D9BA-8BE4-4502-A256-C54BC373A73A@canonical.com>
References: <20200603074819.21639-1-kai.heng.feng@canonical.com>
 <b13888c3-d1f9-7e6e-d25e-0287b3d7ba9b@huawei.com>
To:     John Garry <john.garry@huawei.com>
Sender: linux-kernel-owner@vger.kernel.org
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Hi Jens,

> On Jun 3, 2020, at 16:40, John Garry <john.garry@huawei.com> wrote:
> 
> On 03/06/2020 08:48, 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.
>> Fixes: 130f4caf145c ("libata: Ensure ata_port probe has completed before detach")
>> BugLink: https://bugs.launchpad.net/bugs/1867983
>> Suggested-by: John Garry <john.garry@huawei.com>
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> 
> thanks,
> Tested-by: John Garry <john.garry@huawei.com>

Can you please review or merge this patch?

Kai-Heng

> 
>> ---
>> v3:
>>  - Move the comment to properly align with the code.
>> v2:
>>  - Sync up to cookie + 1.
>>  - Squash the synchronization into the same loop.
>>  drivers/ata/libata-core.c | 11 +++++------
>>  include/linux/libata.h    |  3 +++
>>  2 files changed, 8 insertions(+), 6 deletions(-)
>> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
>> index 69361ec43db5..b1cd4d97bc2a 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;
>> @@ -5920,11 +5919,11 @@ void ata_host_detach(struct ata_host *host)
>>  {
>>  	int i;
>>  -	/* Ensure ata_port probe has completed */
>> -	async_synchronize_full();
>> -
>> -	for (i = 0; i < host->n_ports; i++)
>> +	for (i = 0; i < host->n_ports; i++) {
>> +		/* Ensure ata_port probe has completed */
>> +		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 af832852e620..8a4843704d28 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;
>>  
>