config ROMFS_FS
	tristate "ROM file system support"
	depends on BLOCK || MTD
	---help---
	  This is a very small read-only file system mainly intended for
	  initial ram disks of installation disks, but it could be used for
	  other read-only media as well.  Read
	  <file:Documentation/filesystems/romfs.txt> for details.

	  To compile this file system support as a module, choose M here: the
	  module will be called romfs.  Note that the file system of your
	  root partition (the one containing the directory /) cannot be a
	  module.

	  If you don't know whether you need it, then you don't need it:
	  answer N.

#
# Select the backing stores to be supported
#
choice
	prompt "RomFS backing stores"
	depends on ROMFS_FS
	default ROMFS_BACKED_BY_BLOCK
	help
	  Select the backing stores to be supported.

config ROMFS_BACKED_BY_BLOCK
	bool "Block device-backed ROM file system support"
	depends on BLOCK
	help
	  This permits ROMFS to use block devices buffered through the page
	  cache as the medium from which to retrieve data.  It does not allow
	  direct mapping of the medium.

	  If unsure, answer Y.

config ROMFS_BACKED_BY_MTD
	bool "MTD-backed ROM file system support"
	depends on MTD=y || (ROMFS_FS=m && MTD)
	help
	  This permits ROMFS to use MTD based devices directly, without the
	  intercession of the block layer (which may have been disabled).  It
	  also allows direct mapping of MTD devices through romfs files under
	  NOMMU conditions if the underlying device is directly addressable by
	  the CPU.

	  If unsure, answer Y.

config ROMFS_BACKED_BY_BOTH
	bool "Both the above"
	depends on BLOCK && (MTD=y || (ROMFS_FS=m && MTD))
endchoice


config ROMFS_ON_BLOCK
	bool
	default y if ROMFS_BACKED_BY_BLOCK || ROMFS_BACKED_BY_BOTH

config ROMFS_ON_MTD
	bool
	default y if ROMFS_BACKED_BY_MTD || ROMFS_BACKED_BY_BOTH
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<tr><th>author</th><td>Linus Torvalds &lt;torvalds@linux-foundation.org&gt;</td><td class='right'>2017-01-29 13:50:06 -0800</td></tr>
<tr><th>committer</th><td>Linus Torvalds &lt;torvalds@linux-foundation.org&gt;</td><td class='right'>2017-01-29 13:50:06 -0800</td></tr>
<tr><th>commit</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/net/smc/Makefile?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>39cb2c9a316e77f6dfba96c543e55b6672d5a37e</a> (<a href='/cgit.cgi/linux/net-next.git/patch/net/smc/Makefile?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>patch</a>)</td></tr>
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<div class='commit-subject'>drm/i915: Check for NULL i915_vma in intel_unpin_fb_obj()</div><div class='commit-msg'>I've seen this trigger twice now, where the i915_gem_object_to_ggtt()
call in intel_unpin_fb_obj() returns NULL, resulting in an oops
immediately afterwards as the (inlined) call to i915_vma_unpin_fence()
tries to dereference it.

It seems to be some race condition where the object is going away at
shutdown time, since both times happened when shutting down the X
server.  The call chains were different:

 - VT ioctl(KDSETMODE, KD_TEXT):

    intel_cleanup_plane_fb+0x5b/0xa0 [i915]
    drm_atomic_helper_cleanup_planes+0x6f/0x90 [drm_kms_helper]
    intel_atomic_commit_tail+0x749/0xfe0 [i915]
    intel_atomic_commit+0x3cb/0x4f0 [i915]
    drm_atomic_commit+0x4b/0x50 [drm]
    restore_fbdev_mode+0x14c/0x2a0 [drm_kms_helper]
    drm_fb_helper_restore_fbdev_mode_unlocked+0x34/0x80 [drm_kms_helper]
    drm_fb_helper_set_par+0x2d/0x60 [drm_kms_helper]
    intel_fbdev_set_par+0x18/0x70 [i915]
    fb_set_var+0x236/0x460
    fbcon_blank+0x30f/0x350
    do_unblank_screen+0xd2/0x1a0
    vt_ioctl+0x507/0x12a0
    tty_ioctl+0x355/0xc30
    do_vfs_ioctl+0xa3/0x5e0
    SyS_ioctl+0x79/0x90
    entry_SYSCALL_64_fastpath+0x13/0x94

 - i915 unpin_work workqueue:

    intel_unpin_work_fn+0x58/0x140 [i915]
    process_one_work+0x1f1/0x480
    worker_thread+0x48/0x4d0
    kthread+0x101/0x140

and this patch purely papers over the issue by adding a NULL pointer
check and a WARN_ON_ONCE() to avoid the oops that would then generally
make the machine unresponsive.

Other callers of i915_gem_object_to_ggtt() seem to also check for the
returned pointer being NULL and warn about it, so this clearly has
happened before in other places.

[ Reported it originally to the i915 developers on Jan 8, applying the
  ugly workaround on my own now after triggering the problem for the
  second time with no feedback.

  This is likely to be the same bug reported as

     https://bugs.freedesktop.org/show_bug.cgi?id=98829
     https://bugs.freedesktop.org/show_bug.cgi?id=99134

  which has a patch for the underlying problem, but it hasn't gotten to
  me, so I'm applying the workaround. ]

Cc: Daniel Vetter &lt;daniel.vetter@intel.com&gt;
Cc: Jani Nikula &lt;jani.nikula@linux.intel.com&gt;
Cc: Ville Syrjälä &lt;ville.syrjala@linux.intel.com&gt;
Cc: Chris Wilson &lt;chris@chris-wilson.co.uk&gt;
Cc: Maarten Lankhorst &lt;maarten.lankhorst@linux.intel.com&gt;
Cc: Tvrtko Ursulin &lt;tvrtko.ursulin@intel.com&gt;
Cc: Imre Deak &lt;imre.deak@intel.com&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</div><div class='diffstat-header'><a href='/cgit.cgi/linux/net-next.git/diff/?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>Diffstat</a> (limited to 'net/smc/Makefile')</div><table summary='diffstat' class='diffstat'>