Re: [PATCH v3] libata: Use per port sync for detach

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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@xxxxxxxxxx>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>

thanks,
Tested-by: John Garry <john.garry@xxxxxxxxxx>

---
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;




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