Hi, Yanmin, Thanks for your explain. On Fri, 2012-09-28 at 02:29 -0600, Zhang, Yanmin wrote: > 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. Still has two question. 1. Is it a good practice to hold device_lock when calling driver callback to prevent driver be unbind? 2. Is it a good idea to let callback of pci_walk_bus to acquire device_lock when necessary. Because pci_walk_bus may be used by driver callback too. Best Regards, Huang Ying > -----Original Message----- > From: Huang, Ying > Sent: Friday, September 28, 2012 4:15 PM > To: bhelgaas@xxxxxxxxxx > Cc: Greg Kroah-Hartman; Zhang, Yanmin; linux-pci@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; rjw@xxxxxxx > 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 <yanmin.zhang@xxxxxxxxx> > 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 <yanmin.zhang@xxxxxxxxx> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx> > > 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 > > -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
