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Date: Thu, 26 Jul 2007 19:07:51 -0700 (PDT)
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To: linux-kernel@vger.kernel.org
CC: adobriyan@sw.ru
Subject: /proc/bus/pci IOCTL breakage
From: David Miller <davem@davemloft.net>
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This change:

commit 786d7e1612f0b0adb6046f19b906609e4fe8b1ba
Author: Alexey Dobriyan <adobriyan@sw.ru>
Date:   Sun Jul 15 23:39:00 2007 -0700

    Fix rmmod/read/write races in /proc entries

Broke ioctl() on /proc/bus/pci/* files for COMPAT platforms.

proc_fops->ioctl() is defined for these PCI device files, and the
COMPAT ioctl is handled via fs/compat_ioctl.c's entries, which makes
it just call the ->ioctl() handler directly.

proc_fops->compat_ioctl is NULL for these files, it isn't needed.

This used to work because we used to jump right to the de->proc_fops,
but now we have these wrappers and proc_reg_compat_ioctl is what
gets called and since proc_fops->compat_ioctl is NULL we return
ENOTTY instead of calling proc_fops->ioctl().

Two ways to fix:

1) Make the PROC wrapper call ->unlocked_ioctl() or ->ioctl()
   as a fallback of ->compat_ioctl is NULL.

2) Make proc_bus_pci_operations provide a .compat_ioctl method,
   but then we'll need to audit the entire tree for cases like
   this and make the same fix.

Because it's easier to validate that all cases are covered,
I think #1 is the preferred fix.