srp_queuecommand() can be called from the following contexts: * From inside scsi_queue_rq(). This function can be called by several kernel threads, including the SCSI error handler thread. * From inside scsi_send_eh_cmnd(). This function is only called from the SCSI error handler thread.

In scsi-mq mode it is not allowed to sleep inside srp_queuecommand() since the flag BLK_MQ_F_BLOCKING has not been set. Since setting the request queue flag BLK_MQ_F_BLOCKING would slow down the hot path, make srp_queuecommand() skip the mutex_lock() and mutex_unlock() calls when called from inside scsi_queue_rq() from the SCSI EH thread.

This patch avoids that the following appears in the kernel log:

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:908 in_atomic(): 1, irqs_disabled(): 0, pid: 30974, name: scsi_eh_4 INFO: lockdep is turned off. Preemption disabled at: [<ffffffff816b1d65>] __blk_mq_delay_run_hw_queue+0x185/0x290 CPU: 3 PID: 30974 Comm: scsi_eh_4 Not tainted 4.20.0-rc6-dbg+ #6 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 Call Trace: dump_stack+0x86/0xca ___might_sleep.cold.80+0x128/0x139 __might_sleep+0x71/0xe0 __mutex_lock+0xc8/0xbe0 mutex_lock_nested+0x1b/0x20 srp_queuecommand+0x7f2/0x19a0 [ib_srp] scsi_dispatch_cmd+0x15d/0x510 scsi_queue_rq+0x123/0xa90 blk_mq_dispatch_rq_list+0x678/0xc20 blk_mq_sched_dispatch_requests+0x25c/0x310 __blk_mq_run_hw_queue+0xd6/0x180 __blk_mq_delay_run_hw_queue+0x262/0x290 blk_mq_run_hw_queue+0x11f/0x1b0 blk_mq_run_hw_queues+0x87/0xb0 scsi_run_queue+0x402/0x6f0 scsi_run_host_queues+0x30/0x50 scsi_error_handler+0x2d3/0xa80 kthread+0x1cf/0x1f0 ret_from_fork+0x24/0x30

Cc: Sergey Gorenko sergeygo@mellanox.com Cc: Max Gurtovoy maxg@mellanox.com Cc: Laurence Oberman loberman@redhat.com Cc: stable@vger.kernel.org Fixes: a95cadb9dafe ("IB/srp: Add periodic reconnect functionality") # v3.13 Signed-off-by: Bart Van Assche bvanassche@acm.org --- drivers/infiniband/ulp/srp/ib_srp.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c index 31d91538bbf4..23e5c9afb8fb 100644 --- a/drivers/infiniband/ulp/srp/ib_srp.c +++ b/drivers/infiniband/ulp/srp/ib_srp.c @@ -2352,13 +2352,19 @@ static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd) u32 tag; u16 idx; int len, ret; - const bool in_scsi_eh = !in_interrupt() && current == shost->ehandler; + const bool in_scsi_eh = !in_interrupt() && current == shost->ehandler + && rcu_preempt_depth() == 0;

/* - * The SCSI EH thread is the only context from which srp_queuecommand() - * can get invoked for blocked devices (SDEV_BLOCK / + * The scsi_send_eh_cmnd() function is the only function that can call + * .queuecommand() for blocked devices (SDEV_BLOCK / * SDEV_CREATED_BLOCK). Avoid racing with srp_reconnect_rport() by - * locking the rport mutex if invoked from inside the SCSI EH. + * locking the rport mutex if invoked from inside that function. + * Recognize this context by checking whether called from the SCSI EH + * thread and whether no RCU read lock is held. If + * blk_mq_run_hw_queues() is called from the context of the SCSI EH + * thread then an RCU read lock is held around scsi_queue_rq() calls + * becase the SRP driver does not set BLK_MQ_F_BLOCKING. */ if (in_scsi_eh) mutex_lock(&rport->mutex);