Revision 03049269de433cb5fe2859be9ae4469ceb1163ed authored by Michal Hocko on 25 March 2016, 21:20:33 UTC, committed by Linus Torvalds on 25 March 2016, 23:37:42 UTC
wake_oom_reaper has allowed only 1 oom victim to be queued. The main reason for that was the simplicity as other solutions would require some way of queuing. The current approach is racy and that was deemed sufficient as the oom_reaper is considered a best effort approach to help with oom handling when the OOM victim cannot terminate in a reasonable time. The race could lead to missing an oom victim which can get stuck out_of_memory wake_oom_reaper cmpxchg // OK oom_reaper oom_reap_task __oom_reap_task oom_victim terminates atomic_inc_not_zero // fail out_of_memory wake_oom_reaper cmpxchg // fails task_to_reap = NULL This race requires 2 OOM invocations in a short time period which is not very likely but certainly not impossible. E.g. the original victim might have not released a lot of memory for some reason. The situation would improve considerably if wake_oom_reaper used a more robust queuing. This is what this patch implements. This means adding oom_reaper_list list_head into task_struct (eat a hole before embeded thread_struct for that purpose) and a oom_reaper_lock spinlock for queuing synchronization. wake_oom_reaper will then add the task on the queue and oom_reaper will dequeue it. Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: Vladimir Davydov <vdavydov@virtuozzo.com> Cc: Andrea Argangeli <andrea@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent bc448e8
cordic.c
/*
* Copyright (c) 2011 Broadcom Corporation
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <linux/module.h>
#include <linux/cordic.h>
#define CORDIC_ANGLE_GEN 39797
#define CORDIC_PRECISION_SHIFT 16
#define CORDIC_NUM_ITER (CORDIC_PRECISION_SHIFT + 2)
#define FIXED(X) ((s32)((X) << CORDIC_PRECISION_SHIFT))
#define FLOAT(X) (((X) >= 0) \
? ((((X) >> (CORDIC_PRECISION_SHIFT - 1)) + 1) >> 1) \
: -((((-(X)) >> (CORDIC_PRECISION_SHIFT - 1)) + 1) >> 1))
static const s32 arctan_table[] = {
2949120,
1740967,
919879,
466945,
234379,
117304,
58666,
29335,
14668,
7334,
3667,
1833,
917,
458,
229,
115,
57,
29
};
/*
* cordic_calc_iq() - calculates the i/q coordinate for given angle
*
* theta: angle in degrees for which i/q coordinate is to be calculated
* coord: function output parameter holding the i/q coordinate
*/
struct cordic_iq cordic_calc_iq(s32 theta)
{
struct cordic_iq coord;
s32 angle, valtmp;
unsigned iter;
int signx = 1;
int signtheta;
coord.i = CORDIC_ANGLE_GEN;
coord.q = 0;
angle = 0;
theta = FIXED(theta);
signtheta = (theta < 0) ? -1 : 1;
theta = ((theta + FIXED(180) * signtheta) % FIXED(360)) -
FIXED(180) * signtheta;
if (FLOAT(theta) > 90) {
theta -= FIXED(180);
signx = -1;
} else if (FLOAT(theta) < -90) {
theta += FIXED(180);
signx = -1;
}
for (iter = 0; iter < CORDIC_NUM_ITER; iter++) {
if (theta > angle) {
valtmp = coord.i - (coord.q >> iter);
coord.q += (coord.i >> iter);
angle += arctan_table[iter];
} else {
valtmp = coord.i + (coord.q >> iter);
coord.q -= (coord.i >> iter);
angle -= arctan_table[iter];
}
coord.i = valtmp;
}
coord.i *= signx;
coord.q *= signx;
return coord;
}
EXPORT_SYMBOL(cordic_calc_iq);
MODULE_DESCRIPTION("CORDIC algorithm");
MODULE_AUTHOR("Broadcom Corporation");
MODULE_LICENSE("Dual BSD/GPL");
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