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Subject[PATCH 4.4 018/113] scsi: klist: Make it safe to use klists in atomic context
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bart Van Assche <bart.vanassche@wdc.com>

[ Upstream commit 624fa7790f80575a4ec28fbdb2034097dc18d051 ]

In the scsi_transport_srp implementation it cannot be avoided to
iterate over a klist from atomic context when using the legacy block
layer instead of blk-mq. Hence this patch that makes it safe to use
klists in atomic context. This patch avoids that lockdep reports the
following:

WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
Possible interrupt unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&(&k->k_lock)->rlock);
local_irq_disable();
lock(&(&q->__queue_lock)->rlock);
lock(&(&k->k_lock)->rlock);
<Interrupt>
lock(&(&q->__queue_lock)->rlock);

stack backtrace:
Workqueue: kblockd blk_timeout_work
Call Trace:
dump_stack+0xa4/0xf5
check_usage+0x6e6/0x700
__lock_acquire+0x185d/0x1b50
lock_acquire+0xd2/0x260
_raw_spin_lock+0x32/0x50
klist_next+0x47/0x190
device_for_each_child+0x8e/0x100
srp_timed_out+0xaf/0x1d0 [scsi_transport_srp]
scsi_times_out+0xd4/0x410 [scsi_mod]
blk_rq_timed_out+0x36/0x70
blk_timeout_work+0x1b5/0x220
process_one_work+0x4fe/0xad0
worker_thread+0x63/0x5a0
kthread+0x1c1/0x1e0
ret_from_fork+0x24/0x30

See also commit c9ddf73476ff ("scsi: scsi_transport_srp: Fix shost to
rport translation").

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: James Bottomley <jejb@linux.vnet.ibm.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
lib/klist.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- a/lib/klist.c
+++ b/lib/klist.c
@@ -336,8 +336,9 @@ struct klist_node *klist_prev(struct kli
void (*put)(struct klist_node *) = i->i_klist->put;
struct klist_node *last = i->i_cur;
struct klist_node *prev;
+ unsigned long flags;

- spin_lock(&i->i_klist->k_lock);
+ spin_lock_irqsave(&i->i_klist->k_lock, flags);

if (last) {
prev = to_klist_node(last->n_node.prev);
@@ -356,7 +357,7 @@ struct klist_node *klist_prev(struct kli
prev = to_klist_node(prev->n_node.prev);
}

- spin_unlock(&i->i_klist->k_lock);
+ spin_unlock_irqrestore(&i->i_klist->k_lock, flags);

if (put && last)
put(last);
@@ -377,8 +378,9 @@ struct klist_node *klist_next(struct kli
void (*put)(struct klist_node *) = i->i_klist->put;
struct klist_node *last = i->i_cur;
struct klist_node *next;
+ unsigned long flags;

- spin_lock(&i->i_klist->k_lock);
+ spin_lock_irqsave(&i->i_klist->k_lock, flags);

if (last) {
next = to_klist_node(last->n_node.next);
@@ -397,7 +399,7 @@ struct klist_node *klist_next(struct kli
next = to_klist_node(next->n_node.next);
}

- spin_unlock(&i->i_klist->k_lock);
+ spin_unlock_irqrestore(&i->i_klist->k_lock, flags);

if (put && last)
put(last);

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