/*
 * linux/net/sunrpc/timer.c
 *
 * Estimate RPC request round trip time.
 *
 * Based on packet round-trip and variance estimator algorithms described
 * in appendix A of "Congestion Avoidance and Control" by Van Jacobson
 * and Michael J. Karels (ACM Computer Communication Review; Proceedings
 * of the Sigcomm '88 Symposium in Stanford, CA, August, 1988).
 *
 * This RTT estimator is used only for RPC over datagram protocols.
 *
 * Copyright (C) 2002 Trond Myklebust <trond.myklebust@fys.uio.no>
 */

#include <asm/param.h>

#include <linux/types.h>
#include <linux/unistd.h>
#include <linux/module.h>

#include <linux/sunrpc/clnt.h>

#define RPC_RTO_MAX (60*HZ)
#define RPC_RTO_INIT (HZ/5)
#define RPC_RTO_MIN (HZ/10)

/**
 * rpc_init_rtt - Initialize an RPC RTT estimator context
 * @rt: context to initialize
 * @timeo: initial timeout value, in jiffies
 *
 */
void rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
{
	unsigned long init = 0;
	unsigned int i;

	rt->timeo = timeo;

	if (timeo > RPC_RTO_INIT)
		init = (timeo - RPC_RTO_INIT) << 3;
	for (i = 0; i < 5; i++) {
		rt->srtt[i] = init;
		rt->sdrtt[i] = RPC_RTO_INIT;
		rt->ntimeouts[i] = 0;
	}
}
EXPORT_SYMBOL_GPL(rpc_init_rtt);

/**
 * rpc_update_rtt - Update an RPC RTT estimator context
 * @rt: context to update
 * @timer: timer array index (request type)
 * @m: recent actual RTT, in jiffies
 *
 * NB: When computing the smoothed RTT and standard deviation,
 *     be careful not to produce negative intermediate results.
 */
void rpc_update_rtt(struct rpc_rtt *rt, unsigned int timer, long m)
{
	long *srtt, *sdrtt;

	if (timer-- == 0)
		return;

	/* jiffies wrapped; ignore this one */
	if (m < 0)
		return;

	if (m == 0)
		m = 1L;

	srtt = (long *)&rt->srtt[timer];
	m -= *srtt >> 3;
	*srtt += m;

	if (m < 0)
		m = -m;

	sdrtt = (long *)&rt->sdrtt[timer];
	m -= *sdrtt >> 2;
	*sdrtt += m;

	/* Set lower bound on the variance */
	if (*sdrtt < RPC_RTO_MIN)
		*sdrtt = RPC_RTO_MIN;
}
EXPORT_SYMBOL_GPL(rpc_update_rtt);

/**
 * rpc_calc_rto - Provide an estimated timeout value
 * @rt: context to use for calculation
 * @timer: timer array index (request type)
 *
 * Estimate RTO for an NFS RPC sent via an unreliable datagram.  Use
 * the mean and mean deviation of RTT for the appropriate type of RPC
 * for frequently issued RPCs, and a fixed default for the others.
 *
 * The justification for doing "other" this way is that these RPCs
 * happen so infrequently that timer estimation would probably be
 * stale.  Also, since many of these RPCs are non-idempotent, a
 * conservative timeout is desired.
 *
 * getattr, lookup,
 * read, write, commit     - A+4D
 * other                   - timeo
 */
unsigned long rpc_calc_rto(struct rpc_rtt *rt, unsigned int timer)
{
	unsigned long res;

	if (timer-- == 0)
		return rt->timeo;

	res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
	if (res > RPC_RTO_MAX)
		res = RPC_RTO_MAX;

	return res;
}
EXPORT_SYMBOL_GPL(rpc_calc_rto);
/a>/<a href='/cgit.cgi/linux/net-next.git/commit/net/llc/af_llc.c?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>af_llc.c</a></div><div class='content'><div class='cgit-panel'><b>diff options</b><form method='get'><input type='hidden' name='id' value='39cb2c9a316e77f6dfba96c543e55b6672d5a37e'/><table><tr><td colspan='2'/></tr><tr><td class='label'>context:</td><td class='ctrl'><select name='context' onchange='this.form.submit();'><option value='1'>1</option><option value='2'>2</option><option value='3' selected='selected'>3</option><option value='4'>4</option><option value='5'>5</option><option value='6'>6</option><option value='7'>7</option><option value='8'>8</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/llc/af_llc.c?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>39cb2c9a316e77f6dfba96c543e55b6672d5a37e</a> (<a href='/cgit.cgi/linux/net-next.git/patch/net/llc/af_llc.c?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/llc/af_llc.c?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>net/llc/af_llc.c</a></td></tr>
<tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/net/llc/af_llc.c?id=2c5d9555d6d937966d79d4c6529a5f7b9206e405'>2c5d9555d6d937966d79d4c6529a5f7b9206e405</a> (<a href='/cgit.cgi/linux/net-next.git/diff/net/llc/af_llc.c?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/llc/af_llc.c')</div><table summary='diffstat' class='diffstat'>