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SubjectRe: [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@redhat.com>

Acked-by: Wu Hao <hao.wu@intel.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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