scsi: core: Fix a regression triggered by scsi_host_busy()

In the Linux kernel, the following vulnerability has been resolved: scsi: core: Fix a regression triggered by scsi_host_busy() Commit 995412e23bb2 ("blk-mq: Replace tags->lock with SRCU for tag iterators") introduced the following regression: Call trace: __srcu_read_lock+0x30/0x80 (P) blk_mq_tagset_busy_iter+0x44/0x300 scsi_host_busy+0x38/0x70 ufshcd_print_host_state+0x34/0x1bc ufshcd_link_startup.constprop.0+0xe4/0x2e0 ufshcd_init+0x944/0xf80 ufshcd_pltfrm_init+0x504/0x820 ufs_rockchip_probe+0x2c/0x88 platform_probe+0x5c/0xa4 really_probe+0xc0/0x38c __driver_probe_device+0x7c/0x150 driver_probe_device+0x40/0x120 __driver_attach+0xc8/0x1e0 bus_for_each_dev+0x7c/0xdc driver_attach+0x24/0x30 bus_add_driver+0x110/0x230 driver_register+0x68/0x130 __platform_driver_register+0x20/0x2c ufs_rockchip_pltform_init+0x1c/0x28 do_one_initcall+0x60/0x1e0 kernel_init_freeable+0x248/0x2c4 kernel_init+0x20/0x140 ret_from_fork+0x10/0x20 Fix this regression by making scsi_host_busy() check whether the SCSI host tag set has already been initialized. tag_set->ops is set by scsi_mq_setup_tags() just before blk_mq_alloc_tag_set() is called. This fix is based on the assumption that scsi_host_busy() and scsi_mq_setup_tags() calls are serialized. This is the case in the UFS driver.

Where it's fixed