Re: [PATCH] ata: sata_dwc_460ex: remove incorrect locking

[Julian Margetson <runaway@candw.ms>]

On 12/21/2015 4:41 PM, Andy Shevchenko wrote:
> On Mon, 2015-12-21 at 18:17 +0000, Mans Rullgard wrote:
>> This lock is already taken in ata_scsi_queuecmd() a few levels up the
>> call stack so attempting to take it here is an error.  Moreover, it
>> is
>> pointless in the first place since it only protects a single, atomic
>> assignment.
>>
>> Enabling lock debugging gives the following output:
>>
> +Julian.
>
> I think Julian may give his Tested-by: tag.
>
>> =============================================
>> [ INFO: possible recursive locking detected ]
>> 4.4.0-rc5+ #189 Not tainted
>> ---------------------------------------------
>> kworker/u2:3/37 is trying to acquire lock:
>>   (&(&host->lock)->rlock){-.-...}, at: [<90283294>]
>> sata_dwc_exec_command_by_tag.constprop.14+0x44/0x8c
>>
>> but task is already holding lock:
>>   (&(&host->lock)->rlock){-.-...}, at: [<902761ac>]
>> ata_scsi_queuecmd+0x2c/0x330
>>
>> other info that might help us debug this:
>>   Possible unsafe locking scenario:
>>
>>         CPU0
>>         ----
>>    lock(&(&host->lock)->rlock);
>>    lock(&(&host->lock)->rlock);
>>
>>   *** DEADLOCK ***
>>   May be due to missing lock nesting notation
>>
>> 4 locks held by kworker/u2:3/37:
>>   #0:  ("events_unbound"){.+.+.+}, at: [<9003a0a4>]
>> process_one_work+0x12c/0x430
>>   #1:  ((&entry->work)){+.+.+.}, at: [<9003a0a4>]
>> process_one_work+0x12c/0x430
>>   #2:  (&bdev->bd_mutex){+.+.+.}, at: [<9011fd54>]
>> __blkdev_get+0x50/0x380
>>   #3:  (&(&host->lock)->rlock){-.-...}, at: [<902761ac>]
>> ata_scsi_queuecmd+0x2c/0x330
>>
>> stack backtrace:
>> CPU: 0 PID: 37 Comm: kworker/u2:3 Not tainted 4.4.0-rc5+ #189
>> Workqueue: events_unbound async_run_entry_fn
>> Stack : 90b38e30 00000021 00000003 9b2a6040 00000000 9005f3f0
>> 904fc8dc 00000025
>>          906b96e4 00000000 90528648 9b3336c4 904fc8dc 9009bf18
>> 00000002 00000004
>>          00000000 00000000 9b3336c4 9b3336e4 904fc8dc 9003d074
>> 00000000 90500000
>>          9005e738 00000000 00000000 00000000 00000000 00000000
>> 00000000 00000000
>>          6e657665 755f7374 756f626e 0000646e 00000000 00000000
>> 9b00ca00 9b025000
>>            ...
>> Call Trace:
>> [<90009d6c>] show_stack+0x88/0xa4
>> [<90057744>] __lock_acquire+0x1ce8/0x2154
>> [<900583e4>] lock_acquire+0x64/0x8c
>> [<9045ff10>] _raw_spin_lock_irqsave+0x54/0x78
>> [<90283294>] sata_dwc_exec_command_by_tag.constprop.14+0x44/0x8c
>> [<90283484>] sata_dwc_qc_issue+0x1a8/0x24c
>> [<9026b39c>] ata_qc_issue+0x1f0/0x410
>> [<90273c6c>] ata_scsi_translate+0xb4/0x200
>> [<90276234>] ata_scsi_queuecmd+0xb4/0x330
>> [<9025800c>] scsi_dispatch_cmd+0xd0/0x128
>> [<90259934>] scsi_request_fn+0x58c/0x638
>> [<901a3e50>] __blk_run_queue+0x40/0x5c
>> [<901a83d4>] blk_queue_bio+0x27c/0x28c
>> [<901a5914>] generic_make_request+0xf0/0x188
>> [<901a5a54>] submit_bio+0xa8/0x194
>> [<9011adcc>] submit_bh_wbc.isra.23+0x15c/0x17c
>> [<9011c908>] block_read_full_page+0x3e4/0x428
>> [<9009e2e0>] do_read_cache_page+0xac/0x210
>> [<9009fd90>] read_cache_page+0x18/0x24
>> [<901bbd18>] read_dev_sector+0x38/0xb0
>> [<901bd174>] msdos_partition+0xb4/0x5c0
>> [<901bcb8c>] check_partition+0x140/0x274
>> [<901bba60>] rescan_partitions+0xa0/0x2b0
>> [<9011ff68>] __blkdev_get+0x264/0x380
>> [<901201ac>] blkdev_get+0x128/0x36c
>> [<901b9378>] add_disk+0x3c0/0x4bc
>> [<90268268>] sd_probe_async+0x100/0x224
>> [<90043a44>] async_run_entry_fn+0x50/0x124
>> [<9003a11c>] process_one_work+0x1a4/0x430
>> [<9003a4f4>] worker_thread+0x14c/0x4fc
>> [<900408f4>] kthread+0xd0/0xe8
>> [<90004338>] ret_from_kernel_thread+0x14/0x1c
>>
>> Fixes: 62936009f35a ("[libata] Add 460EX on-chip SATA driver,
>> sata_dwc_460ex")
>> Signed-off-by: Mans Rullgard <mans@mansr.com>
>> ---
>>   drivers/ata/sata_dwc_460ex.c | 4 +---
>>   1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/ata/sata_dwc_460ex.c
>> b/drivers/ata/sata_dwc_460ex.c
>> index 902034991517..7a7faca0ddcd 100644
>> --- a/drivers/ata/sata_dwc_460ex.c
>> +++ b/drivers/ata/sata_dwc_460ex.c
>> @@ -924,15 +924,13 @@ static void sata_dwc_exec_command_by_tag(struct
>> ata_port *ap,
>>   					 struct ata_taskfile *tf,
>>   					 u8 tag, u32 cmd_issued)
>>   {
>> -	unsigned long flags;
>>   	struct sata_dwc_device_port *hsdevp = HSDEVP_FROM_AP(ap);
>>   
>>   	dev_dbg(ap->dev, "%s cmd(0x%02x): %s tag=%d\n", __func__,
>> tf->command,
>>   		ata_get_cmd_descript(tf->command), tag);
>>   
>> -	spin_lock_irqsave(&ap->host->lock, flags);
>>   	hsdevp->cmd_issued[tag] = cmd_issued;
>> -	spin_unlock_irqrestore(&ap->host->lock, flags);
>> +
>>   	/*
>>   	 * Clear SError before executing a new command.
>>   	 * sata_dwc_scr_write and read can not be used here.
>> Clearing the PM

Tested-by: Julian Margetson <runaway@candw.ms>