#ifndef __UNWIND_H
#define __UNWIND_H

#include <linux/types.h>
#include "event.h"
#include "symbol.h"
#include "thread.h"

struct unwind_entry {
	struct map	*map;
	struct symbol	*sym;
	u64		ip;
};

typedef int (*unwind_entry_cb_t)(struct unwind_entry *entry, void *arg);

struct unwind_libunwind_ops {
	int (*prepare_access)(struct thread *thread);
	void (*flush_access)(struct thread *thread);
	void (*finish_access)(struct thread *thread);
	int (*get_entries)(unwind_entry_cb_t cb, void *arg,
			   struct thread *thread,
			   struct perf_sample *data, int max_stack);
};

#ifdef HAVE_DWARF_UNWIND_SUPPORT
int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
			struct thread *thread,
			struct perf_sample *data, int max_stack);
/* libunwind specific */
#ifdef HAVE_LIBUNWIND_SUPPORT
#ifndef LIBUNWIND__ARCH_REG_ID
#define LIBUNWIND__ARCH_REG_ID(regnum) libunwind__arch_reg_id(regnum)
#endif

#ifndef LIBUNWIND__ARCH_REG_SP
#define LIBUNWIND__ARCH_REG_SP PERF_REG_SP
#endif

#ifndef LIBUNWIND__ARCH_REG_IP
#define LIBUNWIND__ARCH_REG_IP PERF_REG_IP
#endif

int LIBUNWIND__ARCH_REG_ID(int regnum);
int unwind__prepare_access(struct thread *thread, struct map *map,
			   bool *initialized);
void unwind__flush_access(struct thread *thread);
void unwind__finish_access(struct thread *thread);
#else
static inline int unwind__prepare_access(struct thread *thread __maybe_unused,
					 struct map *map __maybe_unused,
					 bool *initialized __maybe_unused)
{
	return 0;
}

static inline void unwind__flush_access(struct thread *thread __maybe_unused) {}
static inline void unwind__finish_access(struct thread *thread __maybe_unused) {}
#endif
#else
static inline int
unwind__get_entries(unwind_entry_cb_t cb __maybe_unused,
		    void *arg __maybe_unused,
		    struct thread *thread __maybe_unused,
		    struct perf_sample *data __maybe_unused,
		    int max_stack __maybe_unused)
{
	return 0;
}

static inline int unwind__prepare_access(struct thread *thread __maybe_unused,
					 struct map *map __maybe_unused,
					 bool *initialized __maybe_unused)
{
	return 0;
}

static inline void unwind__flush_access(struct thread *thread __maybe_unused) {}
static inline void unwind__finish_access(struct thread *thread __maybe_unused) {}
#endif /* HAVE_DWARF_UNWIND_SUPPORT */
#endif /* __UNWIND_H */
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<div class='path'>path: <a href='/cgit.cgi/linux/net-next.git/log/?h=nds-private-remove&amp;id=b862815c3ee7b49ec20a9ab25da55a5f0bcbb95e'>root</a>/<a href='/cgit.cgi/linux/net-next.git/log/net?h=nds-private-remove&amp;id=b862815c3ee7b49ec20a9ab25da55a5f0bcbb95e'>net</a>/<a href='/cgit.cgi/linux/net-next.git/log/net/ipv4?h=nds-private-remove&amp;id=b862815c3ee7b49ec20a9ab25da55a5f0bcbb95e'>ipv4</a>/<a href='/cgit.cgi/linux/net-next.git/log/net/ipv4/tcp_illinois.c?h=nds-private-remove&amp;id=b862815c3ee7b49ec20a9ab25da55a5f0bcbb95e'>tcp_illinois.c</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/cgit.cgi/linux/net-next.git/log/net/ipv4/tcp_illinois.c?h=nds-private-remove&amp;id=b862815c3ee7b49ec20a9ab25da55a5f0bcbb95e&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th><th class='left'>Files</th><th class='left'>Lines</th></tr>
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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/include/uapi/asm-generic/Kbuild?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>39cb2c9a316e77f6dfba96c543e55b6672d5a37e</a> (<a href='/cgit.cgi/linux/net-next.git/patch/include/uapi/asm-generic/Kbuild?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>patch</a>)</td></tr>
<tr><th>tree</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/tree/?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>98fe974ee4e20121253de7f61fc8d01bdb3821c1</a> /<a href='/cgit.cgi/linux/net-next.git/tree/include/uapi/asm-generic/Kbuild?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>include/uapi/asm-generic/Kbuild</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 'include/uapi/asm-generic/Kbuild')</div><table summary='diffstat' class='diffstat'>