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scsi: scsi_dh_alua: Avoid crash during alua_bus_detach()

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alua_bus_detach() might be running concurrently with alua_rtpg_work(), so
we might trip over h->sdev == NULL and call BUG_ON().  The correct way of
handling it is to not set h->sdev to NULL in alua_bus_detach(), and call
rcu_synchronize() before the final delete to ensure that all concurrent
threads have left the critical section.  Then we can get rid of the
BUG_ON() and replace it with a simple if condition.

Link: https://lore.kernel.org/r/1600167537-12509-1-git-send-email-jitendra.khasdev@oracle.com
Link: https://lore.kernel.org/r/20200924104559.26753-1-hare@suse.de
Cc: Brian Bunker <brian@purestorage.com>
Acked-by: Brian Bunker <brian@purestorage.com>
Tested-by: Jitendra Khasdev <jitendra.khasdev@oracle.com>
Reviewed-by: Jitendra Khasdev <jitendra.khasdev@oracle.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Hannes Reinecke 2020-09-24 12:45:59 +02:00 committed by Martin K. Petersen
parent af61bc1e33
commit 5faf50e9e9
1 changed files with 5 additions and 4 deletions
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9
drivers/scsi/device_handler/scsi_dh_alua.c
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@ -658,8 +658,8 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
rcu_read_lock();
list_for_each_entry_rcu(h,
&tmp_pg->dh_list, node) {
/* h->sdev should always be valid */
BUG_ON(!h->sdev);
if (!h->sdev)
continue;
h->sdev->access_state = desc[0];
}
rcu_read_unlock();
@ -705,7 +705,8 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
pg->expiry = 0;
rcu_read_lock();
list_for_each_entry_rcu(h, &pg->dh_list, node) {
BUG_ON(!h->sdev);
if (!h->sdev)
continue;
h->sdev->access_state =
(pg->state & SCSI_ACCESS_STATE_MASK);
if (pg->pref)
@ -1147,7 +1148,6 @@ static void alua_bus_detach(struct scsi_device *sdev)
spin_lock(&h->pg_lock);
pg = rcu_dereference_protected(h->pg, lockdep_is_held(&h->pg_lock));
rcu_assign_pointer(h->pg, NULL);
h->sdev = NULL;
spin_unlock(&h->pg_lock);
if (pg) {
spin_lock_irq(&pg->lock);
@ -1156,6 +1156,7 @@ static void alua_bus_detach(struct scsi_device *sdev)
kref_put(&pg->kref, release_port_group);
}
sdev->handler_data = NULL;
synchronize_rcu();
kfree(h);
}