From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 8 Nov 2010 01:12:29 +0000 (+0000)
Subject: drm/i915: Avoid might_fault during pwrite whilst holding our mutex
X-Git-Tag: v2.6.37-rc2~33^2~23^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b47b30ccdaad5f2fc39a1a65921bffd150574a91;p=pandora-kernel.git

drm/i915: Avoid might_fault during pwrite whilst holding our mutex

... and so prevent a potential circular reference:

  [ INFO: possible circular locking dependency detected ]
  2.6.37-rc1-uwe1+ #4
  -------------------------------------------------------
  Xorg/1401 is trying to acquire lock:
   (&mm->mmap_sem){++++++}, at: [<c01e4ddb>] might_fault+0x4b/0xa0

  but task is already holding lock:
   (&dev->struct_mutex){+.+.+.}, at: [<f869c3ac>]
  i915_mutex_lock_interruptible+0x3c/0x60 [i915]

  which lock already depends on the new lock.

When the locking around the pwrite ioctl was simplified, I did not spot
that the phys path never took any locks and so we introduced this
potential circular reference.

Reported-by: Uwe Helm <uwe.helm@googlemail.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---

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