Some error handling functions call pci_walk_bus. For example, pci-e aer. Here we lock the device, so the driver wouldn't detach from the device, as the cb might call driver's callback function.
-----Original Message----- From: Huang, Ying Sent: Friday, September 28, 2012 4:15 PM To: [email protected] Cc: Greg Kroah-Hartman; Zhang, Yanmin; [email protected]; [email protected]; [email protected] Subject: Why hold device_lock when calling callback in pci_walk_bus? Hi, All, If my understanding were correct, device_lock is used to provide mutual exclusion between device probe/remove/suspend/resume etc. Why hold device_lock when calling callback in pci_walk_bus. This is introduced by the following commit. commit d71374dafbba7ec3f67371d3b7e9f6310a588808 Author: Zhang Yanmin <[email protected]> Date: Fri Jun 2 12:35:43 2006 +0800 [PATCH] PCI: fix race with pci_walk_bus and pci_destroy_dev pci_walk_bus has a race with pci_destroy_dev. When cb is called in pci_walk_bus, pci_destroy_dev might unlink the dev pointed by next. Later on in the next loop, pointer next becomes NULL and cause kernel panic. Below patch against 2.6.17-rc4 fixes it by changing pci_bus_lock (spin_lock) to pci_bus_sem (rw_semaphore). Signed-off-by: Zhang Yanmin <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> Corresponding email thread is: https://lkml.org/lkml/2006/5/26/38 But from the commit and email thread, I can not find why we need to do that. I ask this question because I want to use pci_walk_bus in a function (in pci runtime resume path) which may be called with device_lock held. Can anyone help me on that? Best Regards, Huang Ying
