Re: [Linux-kernel-mentees] [PATCH v2 3/3] skd: use generic power management

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On Tue, 2020-07-21 at 12:39 +0530, Vaibhav Gupta wrote:
> On Tue, Jul 21, 2020 at 02:57:28AM +0000, Damien Le Moal wrote:
> > On 2020/07/20 22:32, Vaibhav Gupta wrote:
> > > Drivers using legacy PM have to manage PCI states and device's PM states
> > > themselves. They also need to take care of configuration registers.
> > > 
> > > With improved and powerful support of generic PM, PCI Core takes care of
> > > above mentioned, device-independent, jobs.
> > > 
> > > This driver makes use of PCI helper functions like
> > > pci_save/restore_state(), pci_enable/disable_device(),
> > > pci_request/release_regions(), pci_set_power_state() and
> > > pci_set_master() to do required operations. In generic mode, they are no
> > > longer needed.
> > > 
> > > Change function parameter in both .suspend() and .resume() to
> > > "struct device*" type. Use to_pci_dev() to get "struct pci_dev*" variable.
> > 
> > This commit message is rather vague, and the last sentence actually does not
> > describe correctly the change. What about something very simple, yet clear, like
> > this:
> > 
> > skd: use generic power management
> > 
> > Switch from the legacy .suspend()/.resume() power management interface to the
> > generic power management interface using the single .driver.pm() method. This
> > avoids the need for the driver to directly call most of the PCI helper functions
> > and device power state control functions as the generic power management
> > interface takes care of the necessary operations.
> > 
> Okay. I will improve on it. Just inform me after testing that if any other
> changes are required. I guess [PATCH 1/3] and [PATCH 2/3] are okay, so I will
> only send v3 of [PATCH 3/3] after suggested changes.
> > > Compile-tested only.
> > > 
> > > Signed-off-by: Vaibhav Gupta <vaibhavgupta40@gmail.com>
> > > ---
> > >  drivers/block/skd_main.c | 30 ++++++++----------------------
> > >  1 file changed, 8 insertions(+), 22 deletions(-)
> > > 
> > > diff --git a/drivers/block/skd_main.c b/drivers/block/skd_main.c
> > > index 51569c199a6c..7f2d42900b38 100644
> > > --- a/drivers/block/skd_main.c
> > > +++ b/drivers/block/skd_main.c
> > > @@ -3315,10 +3315,11 @@ static void skd_pci_remove(struct pci_dev *pdev)
> > >  	return;
> > >  }
> > >  
> > > -static int skd_pci_suspend(struct pci_dev *pdev, pm_message_t state)
> > > +static int __maybe_unused skd_pci_suspend(struct device *dev)
> > >  {
> > >  	int i;
> > >  	struct skd_device *skdev;
> > > +	struct pci_dev *pdev = to_pci_dev(dev);
> > >  
> > >  	skdev = pci_get_drvdata(pdev);
> > >  	if (!skdev) {
> > > @@ -3337,18 +3338,15 @@ static int skd_pci_suspend(struct pci_dev *pdev, pm_message_t state)
> > >  	if (skdev->pcie_error_reporting_is_enabled)
> > >  		pci_disable_pcie_error_reporting(pdev);
> > >  
> > > -	pci_release_regions(pdev);
> > > -	pci_save_state(pdev);
> > > -	pci_disable_device(pdev);
> > > -	pci_set_power_state(pdev, pci_choose_state(pdev, state));
> > >  	return 0;
> > >  }
> > >  
> > > -static int skd_pci_resume(struct pci_dev *pdev)
> > > +static int __maybe_unused skd_pci_resume(struct device *dev)
> > >  {
> > >  	int i;
> > >  	int rc = 0;
> > >  	struct skd_device *skdev;
> > > +	struct pci_dev *pdev = to_pci_dev(dev);
> > >  
> > >  	skdev = pci_get_drvdata(pdev);
> > >  	if (!skdev) {
> > > @@ -3356,16 +3354,8 @@ static int skd_pci_resume(struct pci_dev *pdev)
> > >  		return -1;
> > >  	}
> > >  
> > > -	pci_set_power_state(pdev, PCI_D0);
> > > -	pci_enable_wake(pdev, PCI_D0, 0);
> > > -	pci_restore_state(pdev);
> > > +	device_wakeup_disable(dev);
> > >  
> > > -	rc = pci_enable_device(pdev);
> > > -	if (rc)
> > > -		return rc;
> > > -	rc = pci_request_regions(pdev, DRV_NAME);
> > > -	if (rc)
> > > -		goto err_out;
> > >  	rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
> > >  	if (rc)
> > >  		rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
> > > @@ -3374,7 +3364,6 @@ static int skd_pci_resume(struct pci_dev *pdev)
> > >  		goto err_out_regions;
> > >  	}
> > >  
> > > -	pci_set_master(pdev);
> > >  	rc = pci_enable_pcie_error_reporting(pdev);
> > >  	if (rc) {
> > >  		dev_err(&pdev->dev,
> > > @@ -3427,10 +3416,6 @@ static int skd_pci_resume(struct pci_dev *pdev)
> > >  		pci_disable_pcie_error_reporting(pdev);
> > >  
> > >  err_out_regions:
> > > -	pci_release_regions(pdev);
> > > -
> > > -err_out:
> > > -	pci_disable_device(pdev);
> > >  	return rc;
> > >  }
> > >  
> > > @@ -3450,13 +3435,14 @@ static void skd_pci_shutdown(struct pci_dev *pdev)
> > >  	skd_stop_device(skdev);
> > >  }
> > >  
> > > +static SIMPLE_DEV_PM_OPS(skd_pci_pm_ops, skd_pci_suspend, skd_pci_resume);
> > > +
> > >  static struct pci_driver skd_driver = {
> > >  	.name		= DRV_NAME,
> > >  	.id_table	= skd_pci_tbl,
> > >  	.probe		= skd_pci_probe,
> > >  	.remove		= skd_pci_remove,
> > > -	.suspend	= skd_pci_suspend,
> > > -	.resume		= skd_pci_resume,
> > > +	.driver.pm	= &skd_pci_pm_ops,
> > >  	.shutdown	= skd_pci_shutdown,
> > >  };
> > >  
> > > 
> > 
> > Apart from the commit message, this looks OK to me.
> > I will give this a spin today on the hardware to check.
> > 
> Thanks!

Tested this and it seems OK.

Of note, after having removed the device (echo 1 >
/sys/block/skd0/device/remove) and rescaning its PCI slot, I got a
lockdep splat:

[ 4449.098757] ======================================================
[ 4449.104945] WARNING: possible circular locking dependency detected
[ 4449.111136] 5.8.0-rc6+ #846 Not tainted
[ 4449.114980] ------------------------------------------------------
[ 4449.121168] tcsh/1550 is trying to acquire lock:
[ 4449.125798] ffffffffa85c3748 (pci_rescan_remove_lock){+.+.}-{3:3},
at: dev_rescan_store+0x38/0x60
[ 4449.134686] 
[ 4449.134686] but task is already holding lock:
[ 4449.140522] ffff8f6cd352ed28 (kn->active#294){++++}-{0:0}, at:
kernfs_fop_write+0xad/0x1c0
[ 4449.148795] 
[ 4449.148795] which lock already depends on the new lock.
[ 4449.148795] 
[ 4449.156979] 
[ 4449.156979] the existing dependency chain (in reverse order) is:
[ 4449.164464] 
[ 4449.164464] -> #1 (kn->active#294){++++}-{0:0}:
[ 4449.170486]        __kernfs_remove+0x276/0x2f0
[ 4449.174939]        kernfs_remove_by_name_ns+0x41/0x80
[ 4449.180001]        remove_files+0x2b/0x60
[ 4449.184018]        sysfs_remove_group+0x38/0x80
[ 4449.188560]        sysfs_remove_groups+0x29/0x40
[ 4449.193190]        device_remove_attrs+0x4b/0x70
[ 4449.197818]        device_del+0x167/0x3f0
[ 4449.201843]        pci_remove_bus_device+0x70/0x110
[ 4449.206728]        pci_stop_and_remove_bus_device_locked+0x1e/0x30
[ 4449.212915]        remove_store+0x55/0x60
[ 4449.216939]        kernfs_fop_write+0xd9/0x1c0
[ 4449.221398]        vfs_write+0xc7/0x1f0
[ 4449.225239]        ksys_write+0x58/0xd0
[ 4449.229089]        do_syscall_64+0x4f/0x2c0
[ 4449.233284]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 4449.238863] 
[ 4449.238863] -> #0 (pci_rescan_remove_lock){+.+.}-{3:3}:
[ 4449.245575]        __lock_acquire+0x1194/0x1fd0
[ 4449.250113]        lock_acquire+0x97/0x390
[ 4449.254221]        __mutex_lock+0x58/0x820
[ 4449.258330]        dev_rescan_store+0x38/0x60
[ 4449.262697]        kernfs_fop_write+0xd9/0x1c0
[ 4449.267154]        vfs_write+0xc7/0x1f0
[ 4449.270999]        ksys_write+0x58/0xd0
[ 4449.274846]        do_syscall_64+0x4f/0x2c0
[ 4449.279041]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 4449.284620] 
[ 4449.284620] other info that might help us debug this:
[ 4449.284620] 
[ 4449.292628]  Possible unsafe locking scenario:
[ 4449.292628] 
[ 4449.298555]        CPU0                    CPU1
[ 4449.303090]        ----                    ----
[ 4449.307630]   lock(kn->active#294);
[
4449.311131]                                lock(pci_rescan_remove_lock
);
[ 4449.317838]                                lock(kn->active#294);
[ 4449.323855]   lock(pci_rescan_remove_lock);
[ 4449.328048] 
[ 4449.328048]  *** DEADLOCK ***
[ 4449.328048] 
[ 4449.333977] 3 locks held by tcsh/1550:
[ 4449.337731]  #0: ffff8f6f18b7d448 (sb_writers#4){.+.+}-{0:0}, at:
vfs_write+0x174/0x1f0
[ 4449.345747]  #1: ffff8f6e74d09a88 (&of->mutex){+.+.}-{3:3}, at:
kernfs_fop_write+0xa5/0x1c0
[ 4449.354111]  #2: ffff8f6cd352ed28 (kn->active#294){++++}-{0:0}, at:
kernfs_fop_write+0xad/0x1c0
[ 4449.362821] 
[ 4449.362821] stack backtrace:
[ 4449.367192] CPU: 15 PID: 1550 Comm: tcsh Not tainted 5.8.0-rc6+ #846
[ 4449.373548] Hardware name: Supermicro Super Server/X11DPL-i, BIOS
3.1 05/21/2019
[ 4449.380953] Call Trace:
[ 4449.383419]  dump_stack+0x78/0xa0
[ 4449.386744]  check_noncircular+0x12d/0x150
[ 4449.390853]  __lock_acquire+0x1194/0x1fd0
[ 4449.394875]  lock_acquire+0x97/0x390
[ 4449.398462]  ? dev_rescan_store+0x38/0x60
[ 4449.402486]  __mutex_lock+0x58/0x820
[ 4449.406067]  ? dev_rescan_store+0x38/0x60
[ 4449.410090]  ? dev_rescan_store+0x38/0x60
[ 4449.414113]  ? lock_acquire+0x97/0x390
[ 4449.417876]  ? kernfs_fop_write+0xad/0x1c0
[ 4449.421983]  dev_rescan_store+0x38/0x60
[ 4449.425831]  kernfs_fop_write+0xd9/0x1c0
[ 4449.429768]  vfs_write+0xc7/0x1f0
[ 4449.433092]  ksys_write+0x58/0xd0
[ 4449.436421]  do_syscall_64+0x4f/0x2c0
[ 4449.440094]  ? prepare_exit_to_usermode+0xa/0x40
[ 4449.444725]  ? rcu_read_lock_sched_held+0x3f/0x50
[ 4449.449436]  ? asm_exc_page_fault+0x8/0x30
[ 4449.453546]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 4449.458608] RIP: 0033:0x7fcce58f45e7
[ 4449.462191] Code: Bad RIP value.
[ 4449.465426] RSP: 002b:00007fff2592c898 EFLAGS: 00000246 ORIG_RAX:
0000000000000001
[ 4449.473000] RAX: ffffffffffffffda RBX: 0000000000000002 RCX:
00007fcce58f45e7
[ 4449.480141] RDX: 0000000000000002 RSI: 0000556d30b96100 RDI:
0000000000000001
[ 4449.487283] RBP: 0000556d30b96100 R08: 0000000000000000 R09:
00007fff2592c7f0
[ 4449.494425] R10: 0000000000000000 R11: 0000000000000246 R12:
0000000000000001
[ 4449.501567] R13: 0000556d31fc4fb8 R14: 0000556d31fc37c0 R15:
0000556d31fc4fb4
[ 4449.520721] pci 0000:d8:00.0: [1b39:0001] type 00 class 0x018000
[ 4449.526802] pci 0000:d8:00.0: reg 0x10: [mem 0xfbe00000-0xfbe0ffff]
[ 4449.533121] pci 0000:d8:00.0: reg 0x14: [mem 0xfbe10000-0xfbe10fff]
[ 4449.539474] pci 0000:d8:00.0: reg 0x30: [mem 0xfbd00000-0xfbdfffff
pref]
[ 4449.546327] pci 0000:d8:00.0: supports D1 D2
[ 4449.550936] pci 0000:d8:00.0: BAR 6: assigned [mem 0xfbd00000-
0xfbdfffff pref]
[ 4449.559804] pci 0000:d8:00.0: BAR 0: assigned [mem 0xfbe00000-
0xfbe0ffff]
[ 4449.568849] pci 0000:d8:00.0: BAR 1: assigned [mem 0xfbe10000-
0xfbe10fff]
[ 4449.577178] skd 0000:d8:00.0: PCIe (5.0GT/s 4X) 64bit
[ 4449.582272] skd 0000:d8:00.0: bad enable of PCIe error reporting
rc=-5
[ 4449.589764] skd 0000:d8:00.0: s1120 state INIT(1)=>SOFT_RESET(8)
[ 4449.595788] skd 0000:d8:00.0: Driver state STARTING(3)=>STARTING(3)
[ 4449.829900] skd 0000:d8:00.0: s1120 state SOFT_RESET(8)=>INIT(1)
[ 4449.835929] skd 0000:d8:00.0: Driver state STARTING(3)=>STARTING(3)
[ 4450.076148] skd 0000:d8:00.0: Time sync driver=0x5f17d872
device=0x162bdfe9
[ 4450.083139] skd 0000:d8:00.0: s1120 state INIT(1)=>ONLINE(3)
[ 4450.088822] skd 0000:d8:00.0: Queue depth limit=64 dev=255 lowat=43
[ 4450.095101] skd 0000:d8:00.0: Driver state STARTING(3)=>STARTING(3)
[ 4450.101539] skd 0000:d8:00.0: Driver state STARTING(3)=>ONLINE(4)
[ 4450.107653] skd 0000:d8:00.0: STEC s1120 ONLINE
[ 4450.120422]  skd1: p1

But that looks completely unrelated to your patch. Will have a look at
this.

-- 
Damien Le Moal
Western Digital Research
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