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Date:   Thu, 11 Apr 2019 20:43:50 +0800
From:   Wu Hao <hao.wu@...el.com>
To:     Scott Wood <swood@...hat.com>
Cc:     Alan Tull <atull@...nel.org>, Moritz Fischer <mdf@...nel.org>,
        linux-fpga@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fpga: dfl: Add lockdep classes for pdata->lock

Hi Scott,


On Wed, Apr 10, 2019 at 04:53:39PM -0500, Scott Wood wrote:
> struct dfl_feature_platform_data (and it's mutex) is used
> by both fme and port devices, and when lockdep is enabled it
> complains about nesting between these locks.  Tell lockdep about
> the difference so it can track each class separately.
> 
> Here's the lockdep complaint:
> [  409.680668] WARNING: possible recursive locking detected
> [  409.685983] 5.1.0-rc3.fpga+ #1 Tainted: G            E
> [  409.691469] --------------------------------------------
> [  409.696779] fpgaconf/9348 is trying to acquire lock:
> [  409.701746] 00000000a443fe2e (&pdata->lock){+.+.}, at: port_enable_set+0x24/0x60 [dfl_afu]
> [  409.710006]
> [  409.710006] but task is already holding lock:
> [  409.715837] 0000000063b78782 (&pdata->lock){+.+.}, at: fme_pr_ioctl+0x21d/0x330 [dfl_fme]
> [  409.724012]
> [  409.724012] other info that might help us debug this:
> [  409.730535]  Possible unsafe locking scenario:
> [  409.730535]
> [  409.736457]        CPU0
> [  409.738910]        ----
> [  409.741360]   lock(&pdata->lock);
> [  409.744679]   lock(&pdata->lock);
> [  409.747999]
> [  409.747999]  *** DEADLOCK ***
> [  409.747999]
> [  409.753920]  May be due to missing lock nesting notation
> [  409.753920]
> [  409.760704] 4 locks held by fpgaconf/9348:
> [  409.764805]  #0: 0000000063b78782 (&pdata->lock){+.+.}, at: fme_pr_ioctl+0x21d/0x330 [dfl_fme]
> [  409.773408]  #1: 00000000213c8a66 (&region->mutex){+.+.}, at: fpga_region_program_fpga+0x24/0x200 [fpga_region]
> [  409.783489]  #2: 00000000fe63afb9 (&mgr->ref_mutex){+.+.}, at: fpga_mgr_lock+0x15/0x40 [fpga_mgr]
> [  409.792354]  #3: 000000000b2285c5 (&bridge->mutex){+.+.}, at: __fpga_bridge_get+0x26/0xa0 [fpga_bridge]
> [  409.801740]
> [  409.801740] stack backtrace:
> [  409.806102] CPU: 45 PID: 9348 Comm: fpgaconf Kdump: loaded Tainted: G            E     5.1.0-rc3.fpga+ #1
> [  409.815658] Hardware name: Intel Corporation S2600BT/S2600BT, BIOS SE5C620.86B.01.00.0763.022420181017 02/24/2018
> [  409.825911] Call Trace:
> [  409.828369]  dump_stack+0x5e/0x8b
> [  409.831686]  __lock_acquire+0xf3d/0x10e0
> [  409.835612]  ? find_held_lock+0x3c/0xa0
> [  409.839451]  lock_acquire+0xbc/0x1d0
> [  409.843030]  ? port_enable_set+0x24/0x60 [dfl_afu]
> [  409.847823]  ? port_enable_set+0x24/0x60 [dfl_afu]
> [  409.852616]  __mutex_lock+0x86/0x970
> [  409.856195]  ? port_enable_set+0x24/0x60 [dfl_afu]
> [  409.860989]  ? port_enable_set+0x24/0x60 [dfl_afu]
> [  409.865777]  ? __mutex_unlock_slowpath+0x4b/0x290
> [  409.870486]  port_enable_set+0x24/0x60 [dfl_afu]
> [  409.875106]  fpga_bridges_disable+0x36/0x50 [fpga_bridge]
> [  409.880502]  fpga_region_program_fpga+0xea/0x200 [fpga_region]
> [  409.886338]  fme_pr_ioctl+0x13e/0x330 [dfl_fme]
> [  409.890870]  fme_ioctl+0x66/0xe0 [dfl_fme]
> [  409.894973]  do_vfs_ioctl+0xa9/0x720
> [  409.898548]  ? lockdep_hardirqs_on+0xf0/0x1a0
> [  409.902907]  ksys_ioctl+0x60/0x90
> [  409.906225]  __x64_sys_ioctl+0x16/0x20
> [  409.909981]  do_syscall_64+0x5a/0x220
> [  409.913644]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [  409.918698] RIP: 0033:0x7f9d31b9b8d7
> [  409.922276] Code: 44 00 00 48 8b 05 b9 15 2d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 89 15 2d 00 f7 d8 64 89 01 48
> [  409.941020] RSP: 002b:00007ffe4cae0d68 EFLAGS: 00000202 ORIG_RAX: 0000000000000010
> [  409.948588] RAX: ffffffffffffffda RBX: 00007f9d32ade6a0 RCX: 00007f9d31b9b8d7
> [  409.955719] RDX: 00007ffe4cae0df0 RSI: 000000000000b680 RDI: 0000000000000003
> [  409.962852] RBP: 0000000000000003 R08: 00007f9d2b70a177 R09: 00007ffe4cae0e40
> [  409.969984] R10: 00007ffe4cae0160 R11: 0000000000000202 R12: 00007ffe4cae0df0
> [  409.977115] R13: 000000000000b680 R14: 0000000000000000 R15: 00007ffe4cae0f60
> 
> Signed-off-by: Scott Wood <swood@...hat.com>

Acked-by: Wu Hao <hao.wu@...el.com>


Thanks
Hao

> ---
>  drivers/fpga/dfl.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/fpga/dfl.c b/drivers/fpga/dfl.c
> index 2c09e502e721..56dd39dcdcdf 100644
> --- a/drivers/fpga/dfl.c
> +++ b/drivers/fpga/dfl.c
> @@ -40,6 +40,13 @@ enum dfl_fpga_devt_type {
>  	DFL_FPGA_DEVT_MAX,
>  };
>  
> +static struct lock_class_key dfl_pdata_keys[DFL_ID_MAX];
> +
> +static const char *dfl_pdata_key_strings[DFL_ID_MAX] = {
> +	"dfl-fme-pdata",
> +	"dfl-port-pdata",
> +};
> +
>  /**
>   * dfl_dev_info - dfl feature device information.
>   * @name: name string of the feature platform device.
> @@ -443,11 +450,16 @@ static int build_info_commit_dev(struct build_feature_devs_info *binfo)
>  	struct platform_device *fdev = binfo->feature_dev;
>  	struct dfl_feature_platform_data *pdata;
>  	struct dfl_feature_info *finfo, *p;
> +	static enum dfl_id_type type;
>  	int ret, index = 0;
>  
>  	if (!fdev)
>  		return 0;
>  
> +	type = feature_dev_id_type(fdev);
> +	if (WARN_ON_ONCE(type >= DFL_ID_MAX))
> +		return -EINVAL;
> +
>  	/*
>  	 * we do not need to care for the memory which is associated with
>  	 * the platform device. After calling platform_device_unregister(),
> @@ -463,6 +475,8 @@ static int build_info_commit_dev(struct build_feature_devs_info *binfo)
>  	pdata->num = binfo->feature_num;
>  	pdata->dfl_cdev = binfo->cdev;
>  	mutex_init(&pdata->lock);
> +	lockdep_set_class_and_name(&pdata->lock, &dfl_pdata_keys[type],
> +				   dfl_pdata_key_strings[type]);
>  
>  	/*
>  	 * the count should be initialized to 0 to make sure
> @@ -497,7 +511,7 @@ static int build_info_commit_dev(struct build_feature_devs_info *binfo)
>  
>  	ret = platform_device_add(binfo->feature_dev);
>  	if (!ret) {
> -		if (feature_dev_id_type(binfo->feature_dev) == PORT_ID)
> +		if (type == PORT_ID)
>  			dfl_fpga_cdev_add_port_dev(binfo->cdev,
>  						   binfo->feature_dev);
>  		else
> -- 
> 1.8.3.1

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