mainlining shenanigans
95c80bc695
Dongdong reported a deadlock triggered by a hotplug event during a sysfs
"remove" operation:
pciehp 0000:00:0c.0:pcie004: Slot(0-1): Link Up
# echo 1 > 0000:00:0c.0/remove
PME and hotplug share an MSI/MSI-X vector. The sysfs "remove" side is:
remove_store
pci_stop_and_remove_bus_device_locked
pci_lock_rescan_remove
pci_stop_and_remove_bus_device
...
pcie_pme_remove
pcie_pme_suspend
synchronize_irq # wait for hotplug IRQ handler
pci_unlock_rescan_remove
The hotplug side is:
pciehp_ist
pciehp_handle_presence_or_link_change
pciehp_configure_device
pci_lock_rescan_remove # wait for pci_unlock_rescan_remove()
INFO: task bash:10913 blocked for more than 120 seconds.
# ps -ax |grep D
PID TTY STAT TIME COMMAND
10913 ttyAMA0 Ds+ 0:00 -bash
14022 ? D 0:00 [irq/745-pciehp]
# cat /proc/14022/stack
__switch_to+0x94/0xd8
pci_lock_rescan_remove+0x20/0x28
pciehp_configure_device+0x30/0x140
pciehp_handle_presence_or_link_change+0x324/0x458
pciehp_ist+0x1dc/0x1e0
# cat /proc/10913/stack
__switch_to+0x94/0xd8
synchronize_irq+0x8c/0xc0
pcie_pme_suspend+0xa4/0x118
pcie_pme_remove+0x20/0x40
pcie_port_remove_service+0x3c/0x58
...
pcie_port_device_remove+0x2c/0x48
pcie_portdrv_remove+0x68/0x78
pci_device_remove+0x48/0x120
...
pci_stop_bus_device+0x84/0xc0
pci_stop_and_remove_bus_device_locked+0x24/0x40
remove_store+0xa4/0xb8
dev_attr_store+0x44/0x60
sysfs_kf_write+0x58/0x80
It is incorrect to call pcie_pme_suspend() from pcie_pme_remove() for two
reasons.
First, pcie_pme_suspend() calls synchronize_irq(), which will wait for the
native hotplug interrupt handler as well as for the PME one, because they
share one IRQ (as per the spec). That may deadlock if hotplug is signaled
while pcie_pme_remove() is running and the latter calls
pci_lock_rescan_remove() before the former.
Second, if pcie_pme_suspend() figures out that wakeup needs to be enabled
for the port, it will return without disabling the interrupt as expected by
pcie_pme_remove() which was overlooked by commit
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.