/*
 *  net/dccp/qpolicy.c
 *
 *  Policy-based packet dequeueing interface for DCCP.
 *
 *  Copyright (c) 2008 Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License v2
 *  as published by the Free Software Foundation.
 */
#include "dccp.h"

/*
 *	Simple Dequeueing Policy:
 *	If tx_qlen is different from 0, enqueue up to tx_qlen elements.
 */
static void qpolicy_simple_push(struct sock *sk, struct sk_buff *skb)
{
	skb_queue_tail(&sk->sk_write_queue, skb);
}

static bool qpolicy_simple_full(struct sock *sk)
{
	return dccp_sk(sk)->dccps_tx_qlen &&
	       sk->sk_write_queue.qlen >= dccp_sk(sk)->dccps_tx_qlen;
}

static struct sk_buff *qpolicy_simple_top(struct sock *sk)
{
	return skb_peek(&sk->sk_write_queue);
}

/*
 *	Priority-based Dequeueing Policy:
 *	If tx_qlen is different from 0 and the queue has reached its upper bound
 *	of tx_qlen elements, replace older packets lowest-priority-first.
 */
static struct sk_buff *qpolicy_prio_best_skb(struct sock *sk)
{
	struct sk_buff *skb, *best = NULL;

	skb_queue_walk(&sk->sk_write_queue, skb)
		if (best == NULL || skb->priority > best->priority)
			best = skb;
	return best;
}

static struct sk_buff *qpolicy_prio_worst_skb(struct sock *sk)
{
	struct sk_buff *skb, *worst = NULL;

	skb_queue_walk(&sk->sk_write_queue, skb)
		if (worst == NULL || skb->priority < worst->priority)
			worst = skb;
	return worst;
}

static bool qpolicy_prio_full(struct sock *sk)
{
	if (qpolicy_simple_full(sk))
		dccp_qpolicy_drop(sk, qpolicy_prio_worst_skb(sk));
	return false;
}

/**
 * struct dccp_qpolicy_operations  -  TX Packet Dequeueing Interface
 * @push: add a new @skb to the write queue
 * @full: indicates that no more packets will be admitted
 * @top:  peeks at whatever the queueing policy defines as its `top'
 */
static struct dccp_qpolicy_operations {
	void		(*push)	(struct sock *sk, struct sk_buff *skb);
	bool		(*full) (struct sock *sk);
	struct sk_buff*	(*top)  (struct sock *sk);
	__be32		params;

} qpol_table[DCCPQ_POLICY_MAX] = {
	[DCCPQ_POLICY_SIMPLE] = {
		.push   = qpolicy_simple_push,
		.full   = qpolicy_simple_full,
		.top    = qpolicy_simple_top,
		.params = 0,
	},
	[DCCPQ_POLICY_PRIO] = {
		.push   = qpolicy_simple_push,
		.full   = qpolicy_prio_full,
		.top    = qpolicy_prio_best_skb,
		.params = DCCP_SCM_PRIORITY,
	},
};

/*
 *	Externally visible interface
 */
void dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb)
{
	qpol_table[dccp_sk(sk)->dccps_qpolicy].push(sk, skb);
}

bool dccp_qpolicy_full(struct sock *sk)
{
	return qpol_table[dccp_sk(sk)->dccps_qpolicy].full(sk);
}

void dccp_qpolicy_drop(struct sock *sk, struct sk_buff *skb)
{
	if (skb != NULL) {
		skb_unlink(skb, &sk->sk_write_queue);
		kfree_skb(skb);
	}
}

struct sk_buff *dccp_qpolicy_top(struct sock *sk)
{
	return qpol_table[dccp_sk(sk)->dccps_qpolicy].top(sk);
}

struct sk_buff *dccp_qpolicy_pop(struct sock *sk)
{
	struct sk_buff *skb = dccp_qpolicy_top(sk);

	if (skb != NULL) {
		/* Clear any skb fields that we used internally */
		skb->priority = 0;
		skb_unlink(skb, &sk->sk_write_queue);
	}
	return skb;
}

bool dccp_qpolicy_param_ok(struct sock *sk, __be32 param)
{
	/* check if exactly one bit is set */
	if (!param || (param & (param - 1)))
		return false;
	return (qpol_table[dccp_sk(sk)->dccps_qpolicy].params & param) == param;
}
/option><option value='9'>9</option><option value='10'>10</option><option value='15'>15</option><option value='20'>20</option><option value='25'>25</option><option value='30'>30</option><option value='35'>35</option><option value='40'>40</option></select></td></tr><tr><td class='label'>space:</td><td class='ctrl'><select name='ignorews' onchange='this.form.submit();'><option value='0' selected='selected'>include</option><option value='1'>ignore</option></select></td></tr><tr><td class='label'>mode:</td><td class='ctrl'><select name='dt' onchange='this.form.submit();'><option value='0' selected='selected'>unified</option><option value='1'>ssdiff</option><option value='2'>stat only</option></select></td></tr><tr><td/><td class='ctrl'><noscript><input type='submit' value='reload'/></noscript></td></tr></table></form></div><table summary='commit info' class='commit-info'>
<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/sctp?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>39cb2c9a316e77f6dfba96c543e55b6672d5a37e</a> (<a href='/cgit.cgi/linux/net-next.git/patch/net/sctp?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/net/sctp?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>net/sctp</a></td></tr>
<tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/net/sctp?id=2c5d9555d6d937966d79d4c6529a5f7b9206e405'>2c5d9555d6d937966d79d4c6529a5f7b9206e405</a> (<a href='/cgit.cgi/linux/net-next.git/diff/net/sctp?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e&amp;id2=2c5d9555d6d937966d79d4c6529a5f7b9206e405'>diff</a>)</td></tr></table>
<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/sctp')</div><table summary='diffstat' class='diffstat'>