Re: [bug report] lockdep WARN at PCI device rescan

Andy Shevchenko
2023-11-14T12:04:44Z

On Tue, Nov 14, 2023 at 11:47:15AM +0100, Heiner Kallweit wrote:
> On 14.11.2023 11:16, Wolfram Sang wrote:
> > On Tue, Nov 14, 2023 at 06:54:29AM +0000, Shinichiro Kawasaki wrote:
> >> Hello there.
> >>
> >> Recently I tried a couple of commands below on the kernel v6.6 and v6.7-rc1,
> >> then observed a lockdep WARN at the second command [1]. The first command
> >> removes a PCI device, and the second command rescans whole PCI devices to
> >> regain the removed device.
> >>
> >> # echo 1 > /sys/bus/pci/devices/0000:51:00.0/remove
> >> # echo 1 > /sys/bus/pci/rescan
> >>
> >> I tried this rescan for SAS-HBA or AHCI controller with HDDs. When those devices
> >> are left in weird status after some kernel tests, I want to remove the SAS-HBA
> >> and AHCI controller and rescan to get back the devices in good status. This
> >> rescan looks working good except the WARN.
> >>
> >> The lockdep splat indicates possible deadlock between pci_rescan_remove_lock
> >> and work_completion lock have deadlock possibility. Is the lockdep WARN a known
> >> issue? I found a similar discussion in the past [2], but it did not discuss the
> >> work_completion lock, so my observation looks a new, different issue.
> >>
> >> In the call stack, I found that the workqueue thread for i801_probe() calls
> >> p2sb_bar(), which locks pci_rescan_remove_lock. IMHO, the issue cause looks that
> >> pci_rescan_remove_lock is locked in both workqueue context and non-workqueue
> >> context. As a fix trial, I created a quick patch [3]. It calls i801_probe() in
> >> non-workqueue context only by adding a new flag to struct pci_driver. With this,
> >> I observed the lockdep WARN disappears. Is this a good solution approach? If
> >> not, is there any other better solution?

Thanks for the report!

> > Thanks for the report and the proposed solution. I'll add the i801
> > experts, Jean and Heiner, to CC.
>
> + Bjorn, Andy

+ Keith and Lukas as per [2].

> i801 just uses p2sb_bar(), I don't see any issue in i801. Root cause seems to
> be in the PCI subsystem. Calling p2sb_bar() from a PCI driver probe callback
> seems to be problematic, nevertheless it's a valid API usage.

Yeah, the problem is that we have a PCI (kind of) device that needs to be
communicated with in order to instantiate a driver from whatever bus we are
trying to do.

> The proposed fix helps to get an idea of how to work around the issue.
> But IMO it more cures a symptom than fixes the root cause.

I agree, and reading [2] makes me think the same, i.e. that currently this is
a Big PCI lock for everything.

I wanted, before reading [2], to propose to make it nested, but I think it's
not gonna fly,

So, currently I'm lack of (good) ideas and would like to hear other (more
experienced) PCI developers on how is to address this...

> >> [1] kernel message log at the second command
> >>
> >> [ 242.922091] ======================================================
> >> [ 242.931663] WARNING: possible circular locking dependency detected
> >> [ 242.938292] mpt3sas_cm1: 63 BIT PCI BUS DMA ADDRESSING SUPPORTED, total mem (56799464 kB)
> >> [ 242.939415] 6.7.0-rc1-kts #1 Not tainted
> >> [ 242.939419] ------------------------------------------------------
> >> [ 242.939421] bash/1615 is trying to acquire lock:
> >> [ 242.939424] ff1100017bf87910 ((work_completion)(&wfc.work)){+.+.}-{0:0}, at: __flush_work+0xc5/0x980
> >> [ 242.989069]
> >> but task is already holding lock:
> >> [ 243.000283] ffffffff870bf4a8 (pci_rescan_remove_lock){+.+.}-{3:3}, at: rescan_store+0x96/0xd0
> >> [ 243.012269]
> >> which lock already depends on the new lock.
> >>
> >> [ 243.028569]
> >> the existing dependency chain (in reverse order) is:
> >> [ 243.041611]
> >> -> #1 (pci_rescan_remove_lock){+.+.}-{3:3}:
> >> [ 243.053709] __mutex_lock+0x16a/0x1880
> >> [ 243.060767] p2sb_bar+0xa7/0x250
> >> [ 243.067213] i801_add_tco_spt.constprop.0+0x88/0x1f0 [i2c_i801]
> >> [ 243.076707] i801_add_tco+0x18a/0x210 [i2c_i801]
> >> [ 243.084727] i801_probe+0x99c/0x1500 [i2c_i801]
> >> [ 243.092618] local_pci_probe+0xd6/0x190
> >> [ 243.099708] work_for_cpu_fn+0x4e/0xa0
> >> [ 243.106673] process_one_work+0x736/0x1230
> >> [ 243.114012] worker_thread+0x723/0x1300
> >> [ 243.121039] kthread+0x2ee/0x3d0
> >> [ 243.127372] ret_from_fork+0x2d/0x70
> >> [ 243.134073] ret_from_fork_asm+0x1b/0x30
> >> [ 243.141140]
> >> -> #0 ((work_completion)(&wfc.work)){+.+.}-{0:0}:
> >> [ 243.153341] __lock_acquire+0x2e74/0x5ea0
> >> [ 243.160490] lock_acquire+0x196/0x4b0
> >> [ 243.167236] __flush_work+0xe2/0x980
> >> [ 243.173882] work_on_cpu_key+0xcc/0xf0
> >> [ 243.180709] pci_device_probe+0x548/0x740
> >> [ 243.187813] really_probe+0x3df/0xb80
> >> [ 243.194525] __driver_probe_device+0x18c/0x450
> >> [ 243.202128] driver_probe_device+0x4a/0x120
> >> [ 243.209437] __device_attach_driver+0x15e/0x270
> >> [ 243.217149] bus_for_each_drv+0x101/0x170
> >> [ 243.224260] __device_attach+0x189/0x380
> >> [ 243.231254] pci_bus_add_device+0x9f/0xf0
> >> [ 243.238360] pci_bus_add_devices+0x7f/0x190
> >> [ 243.245639] pci_bus_add_devices+0x114/0x190
> >> [ 243.253017] pci_rescan_bus+0x23/0x30
> >> [ 243.259711] rescan_store+0xa2/0xd0
> >> [ 243.266187] kernfs_fop_write_iter+0x356/0x530
> >> [ 243.273735] vfs_write+0x513/0xd60
> >> [ 243.280090] ksys_write+0xe7/0x1b0
> >> [ 243.286412] do_syscall_64+0x5d/0xe0
> >> [ 243.292908] entry_SYSCALL_64_after_hwframe+0x6e/0x76
> >> [ 243.301053]
> >> other info that might help us debug this:
> >>
> >> [ 243.315550] Possible unsafe locking scenario:
> >>
> >> [ 243.325803] CPU0 CPU1
> >> [ 243.332654] ---- ----
> >> [ 243.339492] lock(pci_rescan_remove_lock);
> >> [ 243.345937] lock((work_completion)(&wfc.work));
> >> [ 243.355852] lock(pci_rescan_remove_lock);
> >> [ 243.365170] lock((work_completion)(&wfc.work));
> >> [ 243.372235]
> >> *** DEADLOCK ***
> >>
> >> [ 243.384100] 5 locks held by bash/1615:
> >> [ 243.390048] #0: ff1100013f4b0418 (sb_writers#4){.+.+}-{0:0}, at: ksys_write+0xe7/0x1b0
> >> [ 243.400833] #1: ff11000128429888 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x21d/0x530
> >> [ 243.412623] #2: ff11000103849968 (kn->active#136){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x241/0x530
> >> [ 243.424832] #3: ffffffff870bf4a8 (pci_rescan_remove_lock){+.+.}-{3:3}, at: rescan_store+0x96/0xd0
> >> [ 243.436773] #4: ff1100019cc7e1a8 (&dev->mutex){....}-{3:3}, at: __device_attach+0x67/0x380
> >> [ 243.448048]
> >> stack backtrace:
> >> [ 243.456654] CPU: 16 PID: 1615 Comm: bash Not tainted 6.7.0-rc1-kts #1
> >> [ 243.465797] Hardware name: Supermicro SYS-520P-WTR/X12SPW-TF, BIOS 1.2 02/14/2022
> >> [ 243.476145] Call Trace:
> >> [ 243.480820] <TASK>
> >> [ 243.485084] dump_stack_lvl+0x57/0x90
> >> [ 243.491112] check_noncircular+0x2e1/0x3c0
> >> [ 243.497630] ? __pfx_check_noncircular+0x10/0x10
> >> [ 243.504747] ? __pfx___bfs+0x10/0x10
> >> [ 243.510680] ? lockdep_lock+0xbc/0x1a0
> >> [ 243.516811] ? __pfx_lockdep_lock+0x10/0x10
> >> [ 243.523436] __lock_acquire+0x2e74/0x5ea0
> >> [ 243.529866] ? __pfx___lock_acquire+0x10/0x10
> >> [ 243.536682] lock_acquire+0x196/0x4b0
> >> [ 243.542710] ? __flush_work+0xc5/0x980
> >> [ 243.548829] ? __pfx_lock_acquire+0x10/0x10
> >> [ 243.555442] ? __pfx___lock_acquire+0x10/0x10
> >> [ 243.562252] ? driver_probe_device+0x4a/0x120
> >> [ 243.569061] ? __device_attach_driver+0x15e/0x270
> >> [ 243.576282] ? mark_lock+0xee/0x16c0
> >> [ 243.582222] ? __flush_work+0xc5/0x980
> >> [ 243.588364] __flush_work+0xe2/0x980
> >> [ 243.594300] ? __flush_work+0xc5/0x980
> >> [ 243.600425] ? __queue_work+0x4e4/0xe30
> >> [ 243.606658] ? __pfx___flush_work+0x10/0x10
> >> [ 243.613287] ? lock_is_held_type+0xce/0x120
> >> [ 243.619917] ? queue_work_on+0x69/0xa0
> >> [ 243.626032] ? lockdep_hardirqs_on+0x7d/0x100
> >> [ 243.632834] work_on_cpu_key+0xcc/0xf0
> >> [ 243.638950] ? __pfx_work_on_cpu_key+0x10/0x10
> >> [ 243.645849] ? __pfx_work_for_cpu_fn+0x10/0x10
> >> [ 243.652738] ? __pfx_local_pci_probe+0x10/0x10
> >> [ 243.659638] pci_device_probe+0x548/0x740
> >> [ 243.666057] ? __pfx_pci_device_probe+0x10/0x10
> >> [ 243.673057] ? kernfs_create_link+0x167/0x230
> >> [ 243.679855] really_probe+0x3df/0xb80
> >> [ 243.685860] __driver_probe_device+0x18c/0x450
> >> [ 243.692737] driver_probe_device+0x4a/0x120
> >> [ 243.699314] __device_attach_driver+0x15e/0x270
> >> [ 243.706297] ? __pfx___device_attach_driver+0x10/0x10
> >> [ 243.713890] bus_for_each_drv+0x101/0x170
> >> [ 243.720312] ? __pfx_bus_for_each_drv+0x10/0x10
> >> [ 243.727294] ? lockdep_hardirqs_on+0x7d/0x100
> >> [ 243.734063] ? _raw_spin_unlock_irqrestore+0x35/0x60
> >> [ 243.741505] __device_attach+0x189/0x380
> >> [ 243.747747] ? __pfx___device_attach+0x10/0x10
> >> [ 243.754554] pci_bus_add_device+0x9f/0xf0
> >> [ 243.760836] pci_bus_add_devices+0x7f/0x190
> >> [ 243.767328] pci_bus_add_devices+0x114/0x190
> >> [ 243.773890] pci_rescan_bus+0x23/0x30
> >> [ 243.779741] rescan_store+0xa2/0xd0
> >> [ 243.785362] ? __pfx_rescan_store+0x10/0x10
> >> [ 243.791785] kernfs_fop_write_iter+0x356/0x530
> >> [ 243.798516] vfs_write+0x513/0xd60
> >> [ 243.804054] ? __pfx_vfs_write+0x10/0x10
> >> [ 243.810193] ? __fget_light+0x51/0x220
> >> [ 243.816125] ? __pfx_lock_release+0x10/0x10
> >> [ 243.822555] ksys_write+0xe7/0x1b0
> >> [ 243.828097] ? __pfx_ksys_write+0x10/0x10
> >> [ 243.834327] ? syscall_enter_from_user_mode+0x22/0x90
> >> [ 243.841736] ? lockdep_hardirqs_on+0x7d/0x100
> >> [ 243.848366] do_syscall_64+0x5d/0xe0
> >> [ 243.854114] ? do_syscall_64+0x6c/0xe0
> >> [ 243.860053] ? do_syscall_64+0x6c/0xe0
> >> [ 243.865989] ? lockdep_hardirqs_on+0x7d/0x100
> >> [ 243.872608] ? do_syscall_64+0x6c/0xe0
> >> [ 243.878537] ? lockdep_hardirqs_on+0x7d/0x100
> >> [ 243.885147] entry_SYSCALL_64_after_hwframe+0x6e/0x76
> >> [ 243.892555] RIP: 0033:0x7fee10d53c34
> >> [ 243.898305] Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d 35 77 0d 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 55 48 89 e5 48 83 ec 20 48 89
> >> [ 243.922266] RSP: 002b:00007ffd173e68e8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
> >> [ 243.932655] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007fee10d53c34
> >> [ 243.942564] RDX: 0000000000000002 RSI: 000055f17c9c4bc0 RDI: 0000000000000001
> >> [ 243.952485] RBP: 00007ffd173e6910 R08: 0000000000000073 R09: 0000000000000001
> >> [ 243.962408] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
> >> [ 243.972328] R13: 000055f17c9c4bc0 R14: 00007fee10e245c0 R15: 00007fee10e21f20
> >> [ 243.982259] </TASK>
> >>
> >> [2] https://patchwork.kernel.org/project/linux-pci/patch/20180921205752.3191-1-keith.busch@intel.com/

--
With Best Regards,
Andy Shevchenko