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authorTejun Heo <htejun@gmail.com>2008-05-18 20:15:08 +0400
committerJeff Garzik <jgarzik@redhat.com>2008-05-20 01:51:47 +0400
commitf046519fc85a8fdf6a058b4ac9d897cdee6f3e52 (patch)
treef4ee1fc8edaeaa2fb0245b82925ef40243a9f26f /drivers/ata
parentdc98c32cbe80750ae2d9d9fbdae305d38f005de7 (diff)
downloadlinux-f046519fc85a8fdf6a058b4ac9d897cdee6f3e52.tar.xz
libata: kill hotplug related race condition
Originally, whole reset processing was done while the port is frozen and SError was cleared during @postreset(). This had two race conditions. 1: hotplug could occur after reset but before SError is cleared and libata won't know about it. 2: hotplug could occur after all the reset is complete but before the port is thawed. As all events are cleared on thaw, the hotplug event would be lost. Commit ac371987a81c61c2efbd6931245cdcaf43baad89 kills the first race by clearing SError during link resume but before link onlineness test. However, this doesn't fix race #2 and in some cases clearing SError after SRST is a good idea. This patch solves this problem by cross checking link onlineness with classification result after SError is cleared and port is thawed. Reset is retried if link is online but all devices attached to the link are unknown. As all devices will be revalidated, this one-way check is enough to ensure that all devices are detected and revalidated reliably. This, luckily, also fixes the cases where host controller returns bogus status while harddrive is spinning up after hotplug making classification run before the device sends the first FIS and thus causes misdetection. Low level drivers can bypass the logic by setting class explicitly to ATA_DEV_NONE if ever necessary (currently none requires this). Signed-off-by: Tejun Heo <htejun@gmail.com> Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Diffstat (limited to 'drivers/ata')
-rw-r--r--drivers/ata/libata-core.c21
-rw-r--r--drivers/ata/libata-eh.c52
2 files changed, 50 insertions, 23 deletions
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index c6c316fc8379..ffc689d9e972 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -3490,22 +3490,11 @@ int sata_link_resume(struct ata_link *link, const unsigned long *params,
if ((rc = sata_link_debounce(link, params, deadline)))
return rc;
- /* Clear SError. PMP and some host PHYs require this to
- * operate and clearing should be done before checking PHY
- * online status to avoid race condition (hotplugging between
- * link resume and status check).
- */
+ /* clear SError, some PHYs require this even for SRST to work */
if (!(rc = sata_scr_read(link, SCR_ERROR, &serror)))
rc = sata_scr_write(link, SCR_ERROR, serror);
- if (rc == 0 || rc == -EINVAL) {
- unsigned long flags;
- spin_lock_irqsave(link->ap->lock, flags);
- link->eh_info.serror = 0;
- spin_unlock_irqrestore(link->ap->lock, flags);
- rc = 0;
- }
- return rc;
+ return rc != -EINVAL ? rc : 0;
}
/**
@@ -3704,8 +3693,14 @@ int sata_std_hardreset(struct ata_link *link, unsigned int *class,
*/
void ata_std_postreset(struct ata_link *link, unsigned int *classes)
{
+ u32 serror;
+
DPRINTK("ENTER\n");
+ /* reset complete, clear SError */
+ if (!sata_scr_read(link, SCR_ERROR, &serror))
+ sata_scr_write(link, SCR_ERROR, serror);
+
/* print link status */
sata_print_link_status(link);
diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 06a92c58a49d..751dad0138ae 100644
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -2047,19 +2047,11 @@ static int ata_do_reset(struct ata_link *link, ata_reset_fn_t reset,
unsigned int *classes, unsigned long deadline)
{
struct ata_device *dev;
- int rc;
ata_link_for_each_dev(dev, link)
classes[dev->devno] = ATA_DEV_UNKNOWN;
- rc = reset(link, classes, deadline);
-
- /* convert all ATA_DEV_UNKNOWN to ATA_DEV_NONE */
- ata_link_for_each_dev(dev, link)
- if (classes[dev->devno] == ATA_DEV_UNKNOWN)
- classes[dev->devno] = ATA_DEV_NONE;
-
- return rc;
+ return reset(link, classes, deadline);
}
static int ata_eh_followup_srst_needed(struct ata_link *link,
@@ -2096,7 +2088,7 @@ int ata_eh_reset(struct ata_link *link, int classify,
ata_reset_fn_t reset;
unsigned long flags;
u32 sstatus;
- int rc;
+ int nr_known, rc;
/*
* Prepare to reset
@@ -2245,9 +2237,49 @@ int ata_eh_reset(struct ata_link *link, int classify,
if (ata_is_host_link(link))
ata_eh_thaw_port(ap);
+ /* postreset() should clear hardware SError. Although SError
+ * is cleared during link resume, clearing SError here is
+ * necessary as some PHYs raise hotplug events after SRST.
+ * This introduces race condition where hotplug occurs between
+ * reset and here. This race is mediated by cross checking
+ * link onlineness and classification result later.
+ */
if (postreset)
postreset(link, classes);
+ /* clear cached SError */
+ spin_lock_irqsave(link->ap->lock, flags);
+ link->eh_info.serror = 0;
+ spin_unlock_irqrestore(link->ap->lock, flags);
+
+ /* Make sure onlineness and classification result correspond.
+ * Hotplug could have happened during reset and some
+ * controllers fail to wait while a drive is spinning up after
+ * being hotplugged causing misdetection. By cross checking
+ * link onlineness and classification result, those conditions
+ * can be reliably detected and retried.
+ */
+ nr_known = 0;
+ ata_link_for_each_dev(dev, link) {
+ /* convert all ATA_DEV_UNKNOWN to ATA_DEV_NONE */
+ if (classes[dev->devno] == ATA_DEV_UNKNOWN)
+ classes[dev->devno] = ATA_DEV_NONE;
+ else
+ nr_known++;
+ }
+
+ if (classify && !nr_known && ata_link_online(link)) {
+ if (try < max_tries) {
+ ata_link_printk(link, KERN_WARNING, "link online but "
+ "device misclassified, retrying\n");
+ rc = -EAGAIN;
+ goto fail;
+ }
+ ata_link_printk(link, KERN_WARNING,
+ "link online but device misclassified, "
+ "device detection might fail\n");
+ }
+
/* reset successful, schedule revalidation */
ata_eh_done(link, NULL, ATA_EH_RESET);
ehc->i.action |= ATA_EH_REVALIDATE;