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SubjectRE: [PATCH 2/5 V4] PCI: pciehp: check and wait port status out of DPC before handling DLLSC and PDC
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Sathyanarayanan,

-----Original Message-----
From: Kuppuswamy, Sathyanarayanan <sathyanarayanan.kuppuswamy@intel.com>
Sent: Monday, September 28, 2020 2:59 AM
To: Zhao, Haifeng <haifeng.zhao@intel.com>; bhelgaas@google.com; oohall@gmail.com; ruscur@russell.cc; lukas@wunner.de; andriy.shevchenko@linux.intel.com; stuart.w.hayes@gmail.com; mr.nuke.me@gmail.com; mika.westerberg@linux.intel.com
Cc: linux-pci@vger.kernel.org; linux-kernel@vger.kernel.org; Jia, Pei P <pei.p.jia@intel.com>; ashok.raj@linux.intel.com; hch@infradead.org; joe@perches.com
Subject: Re: [PATCH 2/5 V4] PCI: pciehp: check and wait port status out of DPC before handling DLLSC and PDC


On 9/27/20 1:27 AM, Ethan Zhao wrote:
> When root port has DPC capability and it is enabled, then triggered by
> errors, DPC DLLSC and PDC interrupts will be sent to DPC driver,
> pciehp driver at the same time.
> That will cause following result:
>
> 1. Link and device are recovered by hardware DPC and software DPC driver,
> device
> isn't removed, but the pciehp might treat it as device was hot removed.
>
> 2. Race condition happens bettween pciehp_unconfigure_device() called by
> pciehp_ist() in pciehp driver and pci_do_recovery() called by
> dpc_handler in DPC driver. no luck, there is no lock to protect
> pci_stop_and_remove_bus_device()
> against pci_walk_bus(), they hold different samphore and mutex,
> pci_stop_and_remove_bus_device holds pci_rescan_remove_lock, and
> pci_walk_bus() holds pci_bus_sem.
Why not address the locking issue? May be a common lock?
>
> This race condition is not purely code analysis, it could be triggered
> by following command series:
>
> # setpci -s 64:02.0 0x196.w=000a // 64:02.0 rootport has DPC capability
> # setpci -s 65:00.0 0x04.w=0544 // 65:00.0 NVMe SSD populated in port
> # mount /dev/nvme0n1p1 nvme
>
> One shot will cause system panic and NULL pointer reference happened.
> (tested on stable 5.8 & ICS(Ice Lake SP platform, see
> https://en.wikichip.org/wiki/intel/microarchitectures/ice_lake_(server
> ))
>
> Buffer I/O error on dev nvme0n1p1, logical block 3328, async page read
> BUG: kernel NULL pointer dereference, address: 0000000000000050
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 0
> Oops: 0000 [#1] SMP NOPTI
> CPU: 12 PID: 513 Comm: irq/124-pcie-dp Not tainted 5.8.0 el8.x86_64+ #1
> RIP: 0010:report_error_detected.cold.4+0x7d/0xe6
> Code: b6 d0 e8 e8 fe 11 00 e8 16 c5 fb ff be 06 00 00 00 48 89 df e8 d3
> 65 ff ff b8 06 00 00 00 e9 75 fc ff ff 48 8b 43 68 45 31 c9 <48> 8b 50
> 50 48 83 3a 00 41 0f 94 c1 45 31 c0 48 85 d2 41 0f 94 c0
> RSP: 0018:ff8e06cf8762fda8 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ff4e3eaacf42a000 RCX: ff4e3eb31f223c01
> RDX: ff4e3eaacf42a140 RSI: ff4e3eb31f223c00 RDI: ff4e3eaacf42a138
> RBP: ff8e06cf8762fdd0 R08: 00000000000000bf R09: 0000000000000000
> R10: 000000eb8ebeab53 R11: ffffffff93453258 R12: 0000000000000002
> R13: ff4e3eaacf42a130 R14: ff8e06cf8762fe2c R15: ff4e3eab44733828
> FS: 0000000000000000(0000) GS:ff4e3eab1fd00000(0000) knl
> GS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000050 CR3: 0000000f8f80a004 CR4: 0000000000761ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
> ? report_normal_detected+0x20/0x20
> report_frozen_detected+0x16/0x20
> pci_walk_bus+0x75/0x90
> ? dpc_irq+0x90/0x90
> pcie_do_recovery+0x157/0x201
> ? irq_finalize_oneshot.part.47+0xe0/0xe0
> dpc_handler+0x29/0x40
> irq_thread_fn+0x24/0x60
> irq_thread+0xea/0x170
> ? irq_forced_thread_fn+0x80/0x80
> ? irq_thread_check_affinity+0xf0/0xf0
> kthread+0x124/0x140
> ? kthread_park+0x90/0x90
> ret_from_fork+0x1f/0x30
> Modules linked in: nft_fib_inet.........
> CR2: 0000000000000050
>
> With this patch, the handling flow of DPC containment and hotplug is
> partly ordered and serialized,
If its a partial fix, what scenario is not covered?


:see the 1/5 patch.

> let hardware DPC do the controller reset etc recovery action first,
> then DPC driver handling the call-back from device drivers, clear the
> DPC status, at the end, pciehp handle the DLLSC and PDC etc.
>
> Signed-off-by: Ethan Zhao <haifeng.zhao@intel.com>
> Tested-by: Wen Jin <wen.jin@intel.com>
> Tested-by: Shanshan Zhang <ShanshanX.Zhang@intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> Changes:
> V2: revise doc according to Andy's suggestion.
> V3: no change.
> V4: no change.
>
> drivers/pci/hotplug/pciehp_hpc.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c
> b/drivers/pci/hotplug/pciehp_hpc.c
> index 53433b37e181..6f271160f18d 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -710,8 +710,10 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id)
> down_read(&ctrl->reset_lock);
> if (events & DISABLE_SLOT)
> pciehp_handle_disable_request(ctrl);
> - else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC))
> + else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC)) {
> + pci_wait_port_outdpc(pdev);
This would add worst case 1s delay in handling the DLLSC events. This does not distinguish between DLLSC event triggered by DPC or hotplug. Also additional delay may violate the timing requirements.
: It will wait only when DPC is enabled and triggered. Or it will skip the waiting.
Test with different time interval between hot-remove and hot-plugin, also no spec
Says it will violate timing requirement. It works.

Thanks,
Ethan

> pciehp_handle_presence_or_link_change(ctrl, events);
> + }
> up_read(&ctrl->reset_lock);
>
> ret = IRQ_HANDLED;

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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