Re: [PATCH AUTOSEL 5.1 16/59] fpga: dfl: Add lockdep classes for pdata->lock

[Sasha Levin]

On Sat, Jun 15, 2019 at 07:47:39AM +0200, Greg Kroah-Hartman wrote:
> On Fri, Jun 14, 2019 at 04:28:00PM -0400, Sasha Levin wrote:
> > From: Scott Wood <swood@xxxxxxxxxx>
> >
> > [ Upstream commit dfe3de8d397bf878b31864d4e489d41118ec475f ]
> >
> > 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@xxxxxxxxxx>
> > Acked-by: Wu Hao <hao.wu@xxxxxxxxx>
> > Acked-by: Alan Tull <atull@xxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> >  drivers/fpga/dfl.c | 16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
>
> Adding lockdep stuff is not really needed for stable kernels, please
> drop this from all trees.

For actual splats? Why? I treat them as compiler warnings. Keeping these
around will just make them show up over and over in testing (at least
until we unify our testing story...).

--
Thanks,
Sasha