From: Christoph Hellwig <[email protected]> 3.12-stable review patch. If anyone has any objections, please let me know.
=============== commit 40998193560dab6c3ce8d25f4fa58a23e252ef38 upstream. When dropping a lock while iterating a list we must restart the search as other threads could have manipulated the list under us. Without this we can get stuck in an endless loop. This bug was introduced by commit bc3f02a795d3b4faa99d37390174be2a75d091bd Author: Dan Williams <[email protected]> Date: Tue Aug 28 22:12:10 2012 -0700 [SCSI] scsi_remove_target: fix softlockup regression on hot remove Which was itself trying to fix a reported soft lockup issue http://thread.gmane.org/gmane.linux.kernel/1348679 However, we believe even with this revert of the original patch, the soft lockup problem has been fixed by commit f2495e228fce9f9cec84367547813cbb0d6db15a Author: James Bottomley <[email protected]> Date: Tue Jan 21 07:01:41 2014 -0800 [SCSI] dual scan thread bug fix Thanks go to Dan Williams <[email protected]> for tracking all this prior history down. Reported-by: Johannes Thumshirn <[email protected]> Signed-off-by: Christoph Hellwig <[email protected]> Tested-by: Johannes Thumshirn <[email protected]> Reviewed-by: Johannes Thumshirn <[email protected]> Fixes: bc3f02a795d3b4faa99d37390174be2a75d091bd Signed-off-by: James Bottomley <[email protected]> Signed-off-by: Jiri Slaby <[email protected]> --- drivers/scsi/scsi_sysfs.c | 16 ++++------------ 1 file changed, 4 insertions(+), 12 deletions(-) diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index dfb007c95b98..678a9f96588a 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -1070,31 +1070,23 @@ static void __scsi_remove_target(struct scsi_target *starget) void scsi_remove_target(struct device *dev) { struct Scsi_Host *shost = dev_to_shost(dev->parent); - struct scsi_target *starget, *last = NULL; + struct scsi_target *starget; unsigned long flags; - /* remove targets being careful to lookup next entry before - * deleting the last - */ +restart: spin_lock_irqsave(shost->host_lock, flags); list_for_each_entry(starget, &shost->__targets, siblings) { if (starget->state == STARGET_DEL) continue; if (starget->dev.parent == dev || &starget->dev == dev) { - /* assuming new targets arrive at the end */ kref_get(&starget->reap_ref); spin_unlock_irqrestore(shost->host_lock, flags); - if (last) - scsi_target_reap(last); - last = starget; __scsi_remove_target(starget); - spin_lock_irqsave(shost->host_lock, flags); + scsi_target_reap(starget); + goto restart; } } spin_unlock_irqrestore(shost->host_lock, flags); - - if (last) - scsi_target_reap(last); } EXPORT_SYMBOL(scsi_remove_target); -- 2.7.1
