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
name.c
// SPDX-License-Identifier: GPL-2.0
/*
* linux/fs/hpfs/name.c
*
* Mikulas Patocka (mikulas@artax.karlin.mff.cuni.cz), 1998-1999
*
* operations with filenames
*/
#include "hpfs_fn.h"
static inline int not_allowed_char(unsigned char c)
{
return c<' ' || c=='"' || c=='*' || c=='/' || c==':' || c=='<' ||
c=='>' || c=='?' || c=='\\' || c=='|';
}
static inline int no_dos_char(unsigned char c)
{ /* Characters that are allowed in HPFS but not in DOS */
return c=='+' || c==',' || c==';' || c=='=' || c=='[' || c==']';
}
static inline unsigned char upcase(unsigned char *dir, unsigned char a)
{
if (a<128 || a==255) return a>='a' && a<='z' ? a - 0x20 : a;
if (!dir) return a;
return dir[a-128];
}
unsigned char hpfs_upcase(unsigned char *dir, unsigned char a)
{
return upcase(dir, a);
}
static inline unsigned char locase(unsigned char *dir, unsigned char a)
{
if (a<128 || a==255) return a>='A' && a<='Z' ? a + 0x20 : a;
if (!dir) return a;
return dir[a];
}
int hpfs_chk_name(const unsigned char *name, unsigned *len)
{
int i;
if (*len > 254) return -ENAMETOOLONG;
hpfs_adjust_length(name, len);
if (!*len) return -EINVAL;
for (i = 0; i < *len; i++) if (not_allowed_char(name[i])) return -EINVAL;
if (*len == 1) if (name[0] == '.') return -EINVAL;
if (*len == 2) if (name[0] == '.' && name[1] == '.') return -EINVAL;
return 0;
}
unsigned char *hpfs_translate_name(struct super_block *s, unsigned char *from,
unsigned len, int lc, int lng)
{
unsigned char *to;
int i;
if (hpfs_sb(s)->sb_chk >= 2) if (hpfs_is_name_long(from, len) != lng) {
pr_err("Long name flag mismatch - name ");
for (i = 0; i < len; i++)
pr_cont("%c", from[i]);
pr_cont(" misidentified as %s.\n", lng ? "short" : "long");
pr_err("It's nothing serious. It could happen because of bug in OS/2.\nSet checks=normal to disable this message.\n");
}
if (!lc) return from;
if (!(to = kmalloc(len, GFP_KERNEL))) {
pr_err("can't allocate memory for name conversion buffer\n");
return from;
}
for (i = 0; i < len; i++) to[i] = locase(hpfs_sb(s)->sb_cp_table,from[i]);
return to;
}
int hpfs_compare_names(struct super_block *s,
const unsigned char *n1, unsigned l1,
const unsigned char *n2, unsigned l2, int last)
{
unsigned l = l1 < l2 ? l1 : l2;
unsigned i;
if (last) return -1;
for (i = 0; i < l; i++) {
unsigned char c1 = upcase(hpfs_sb(s)->sb_cp_table,n1[i]);
unsigned char c2 = upcase(hpfs_sb(s)->sb_cp_table,n2[i]);
if (c1 < c2) return -1;
if (c1 > c2) return 1;
}
if (l1 < l2) return -1;
if (l1 > l2) return 1;
return 0;
}
int hpfs_is_name_long(const unsigned char *name, unsigned len)
{
int i,j;
for (i = 0; i < len && name[i] != '.'; i++)
if (no_dos_char(name[i])) return 1;
if (!i || i > 8) return 1;
if (i == len) return 0;
for (j = i + 1; j < len; j++)
if (name[j] == '.' || no_dos_char(name[i])) return 1;
return j - i > 4;
}
/* OS/2 clears dots and spaces at the end of file name, so we have to */
void hpfs_adjust_length(const unsigned char *name, unsigned *len)
{
if (!*len) return;
if (*len == 1 && name[0] == '.') return;
if (*len == 2 && name[0] == '.' && name[1] == '.') return;
while (*len && (name[*len - 1] == '.' || name[*len - 1] == ' '))
(*len)--;
}
Computing file changes ...
