[PATCH 0/3] SCSI: Fix hard lockup in scsi_remove_target()

[Johannes Thumshirn <jthumshirn@suse.de>]

Removing a SCSI target via scsi_remove_target() suspected to be racy. When a
sibling get's removed from the list it can occassionly happen that one CPU is
stuck endlessly looping around this code block

list_for_each_entry(starget, &shost->__targets, siblings) {
        if (starget->state == STARGET_DEL)
                continue;

Resulting in the following hard lockup.

Kernel panic - not syncing: Watchdog detected hard LOCKUP on cpu 0
[...]
Call Trace:
 [<ffffffff8100471d>] dump_trace+0x7d/0x2d0
 [<ffffffff81004a04>] show_stack_log_lvl+0x94/0x170
 [<ffffffff81005cc1>] show_stack+0x21/0x50
 [<ffffffff8151aa75>] dump_stack+0x41/0x51
 [<ffffffff8151545a>] panic+0xc8/0x1d7
 [<ffffffff810fbdda>] watchdog_overflow_callback+0xba/0xc0
 [<ffffffff811336c8>] __perf_event_overflow+0x88/0x240
 [<ffffffff8101e3aa>] intel_pmu_handle_irq+0x1fa/0x3e0
 [<ffffffff81522836>] perf_event_nmi_handler+0x26/0x40
 [<ffffffff81521fcd>] nmi_handle.isra.2+0x8d/0x180
 [<ffffffff815221e6>] do_nmi+0x126/0x3c0
 [<ffffffff8152159b>] end_repeat_nmi+0x1a/0x1e
 [<ffffffffa00212e8>] scsi_remove_target+0x68/0x240 [scsi_mod]
 [<ffffffff81072742>] process_one_work+0x172/0x420
 [<ffffffff810733ba>] worker_thread+0x11a/0x3c0
 [<ffffffff81079d34>] kthread+0xb4/0xc0
 [<ffffffff81528cd8>] ret_from_fork+0x58/0x90

This series attacks the issue by 1) decoupling the __targets and __devices
lists of struct Scsi_Host from the host_lock spinlock by introducing spinlocks
for each list and 2) de-coupling the list traversals needed for detecting
targets/devices to be removed from the actual removal by moving list entries to
be deleted to a second list and perform the deletion there.


The whole series survived a nearly 48h test loop of:
while [ $not_done  ]; do
	umount $mountpoint;
	rmmod $module;
	modprobe $module;
	mount $mountpoint;
done

This is a follow up of the patch proposed here:
http://marc.info/?l=linux-scsi&m=144377409311774&w=2
incorporating Christoph's comment

Johannes Thumshirn (3):
  SCSI: Introduce device_lock and target_lock in Scsi_Host
  SCSI: Rework list handling in scsi_target_remove
  SCSI: Rework list handling in __scsi_target_remove

 drivers/scsi/53c700.c     |  3 +++
 drivers/scsi/hosts.c      |  2 ++
 drivers/scsi/scsi.c       |  8 ++++----
 drivers/scsi/scsi_scan.c  | 10 +++++-----
 drivers/scsi/scsi_sysfs.c | 43 +++++++++++++++++++++----------------------
 include/scsi/scsi_host.h  |  2 ++
 6 files changed, 37 insertions(+), 31 deletions(-)

-- 
1.8.5.6