Revision 6e2df0581f569038719cf2bc2b3baa3fcc83cab4 authored by Peter Zijlstra on 08 November 2019, 10:11:52 UTC, committed by Peter Zijlstra on 08 November 2019, 21:34:14 UTC
Commit 67692435c411 ("sched: Rework pick_next_task() slow-path") inadvertly introduced a race because it changed a previously unexplored dependency between dropping the rq->lock and sched_class::put_prev_task(). The comments about dropping rq->lock, in for example newidle_balance(), only mentions the task being current and ->on_cpu being set. But when we look at the 'change' pattern (in for example sched_setnuma()): queued = task_on_rq_queued(p); /* p->on_rq == TASK_ON_RQ_QUEUED */ running = task_current(rq, p); /* rq->curr == p */ if (queued) dequeue_task(...); if (running) put_prev_task(...); /* change task properties */ if (queued) enqueue_task(...); if (running) set_next_task(...); It becomes obvious that if we do this after put_prev_task() has already been called on @p, things go sideways. This is exactly what the commit in question allows to happen when it does: prev->sched_class->put_prev_task(rq, prev, rf); if (!rq->nr_running) newidle_balance(rq, rf); The newidle_balance() call will drop rq->lock after we've called put_prev_task() and that allows the above 'change' pattern to interleave and mess up the state. Furthermore, it turns out we lost the RT-pull when we put the last DL task. Fix both problems by extracting the balancing from put_prev_task() and doing a multi-class balance() pass before put_prev_task(). Fixes: 67692435c411 ("sched: Rework pick_next_task() slow-path") Reported-by: Quentin Perret <qperret@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Quentin Perret <qperret@google.com> Tested-by: Valentin Schneider <valentin.schneider@arm.com>
1 parent e3b8b6a
lzo_wrapper.c
// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Squashfs - a compressed read only filesystem for Linux
*
* Copyright (c) 2010 LG Electronics
* Chan Jeong <chan.jeong@lge.com>
*
* lzo_wrapper.c
*/
#include <linux/mutex.h>
#include <linux/buffer_head.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/lzo.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs.h"
#include "decompressor.h"
#include "page_actor.h"
struct squashfs_lzo {
void *input;
void *output;
};
static void *lzo_init(struct squashfs_sb_info *msblk, void *buff)
{
int block_size = max_t(int, msblk->block_size, SQUASHFS_METADATA_SIZE);
struct squashfs_lzo *stream = kzalloc(sizeof(*stream), GFP_KERNEL);
if (stream == NULL)
goto failed;
stream->input = vmalloc(block_size);
if (stream->input == NULL)
goto failed;
stream->output = vmalloc(block_size);
if (stream->output == NULL)
goto failed2;
return stream;
failed2:
vfree(stream->input);
failed:
ERROR("Failed to allocate lzo workspace\n");
kfree(stream);
return ERR_PTR(-ENOMEM);
}
static void lzo_free(void *strm)
{
struct squashfs_lzo *stream = strm;
if (stream) {
vfree(stream->input);
vfree(stream->output);
}
kfree(stream);
}
static int lzo_uncompress(struct squashfs_sb_info *msblk, void *strm,
struct buffer_head **bh, int b, int offset, int length,
struct squashfs_page_actor *output)
{
struct squashfs_lzo *stream = strm;
void *buff = stream->input, *data;
int avail, i, bytes = length, res;
size_t out_len = output->length;
for (i = 0; i < b; i++) {
avail = min(bytes, msblk->devblksize - offset);
memcpy(buff, bh[i]->b_data + offset, avail);
buff += avail;
bytes -= avail;
offset = 0;
put_bh(bh[i]);
}
res = lzo1x_decompress_safe(stream->input, (size_t)length,
stream->output, &out_len);
if (res != LZO_E_OK)
goto failed;
res = bytes = (int)out_len;
data = squashfs_first_page(output);
buff = stream->output;
while (data) {
if (bytes <= PAGE_SIZE) {
memcpy(data, buff, bytes);
break;
} else {
memcpy(data, buff, PAGE_SIZE);
buff += PAGE_SIZE;
bytes -= PAGE_SIZE;
data = squashfs_next_page(output);
}
}
squashfs_finish_page(output);
return res;
failed:
return -EIO;
}
const struct squashfs_decompressor squashfs_lzo_comp_ops = {
.init = lzo_init,
.free = lzo_free,
.decompress = lzo_uncompress,
.id = LZO_COMPRESSION,
.name = "lzo",
.supported = 1
};
![swh spinner](/static/img/swh-spinner.gif)
Computing file changes ...