2014-10-16 10:39:44

by Kirill Tkhai

[permalink] [raw]
Subject: [PATCH] sched/fair: Fix division by zero sysctl_numa_balancing_scan_size


File /proc/sys/kernel/numa_balancing_scan_size_mb allows writing of zero.

This bash command reproduces problem:

$ while :; do echo 0 > /proc/sys/kernel/numa_balancing_scan_size_mb; \
echo 256 > /proc/sys/kernel/numa_balancing_scan_size_mb; done

divide error: 0000 [#1] SMP
Modules linked in:
CPU: 0 PID: 24112 Comm: bash Not tainted 3.17.0+ #8
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88013c852600 ti: ffff880037a68000 task.ti: ffff880037a68000
RIP: 0010:[<ffffffff81074191>] [<ffffffff81074191>] task_scan_min+0x21/0x50
RSP: 0000:ffff880037a6bce0 EFLAGS: 00010246
RAX: 0000000000000a00 RBX: 00000000000003e8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88013c852600
RBP: ffff880037a6bcf0 R08: 0000000000000001 R09: 0000000000015c90
R10: ffff880239bf6c00 R11: 0000000000000016 R12: 0000000000003fff
R13: ffff88013c852600 R14: ffffea0008d1b000 R15: 0000000000000003
FS: 00007f12bb048700(0000) GS:ffff88007da00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000001505678 CR3: 0000000234770000 CR4: 00000000000006f0
Stack:
ffff88013c852600 0000000000003fff ffff880037a6bd18 ffffffff810741d1
ffff88013c852600 0000000000003fff 000000000002bfff ffff880037a6bda8
ffffffff81077ef7 ffffea0008a56d40 0000000000000001 0000000000000001
Call Trace:
[<ffffffff810741d1>] task_scan_max+0x11/0x40
[<ffffffff81077ef7>] task_numa_fault+0x1f7/0xae0
[<ffffffff8115a896>] ? migrate_misplaced_page+0x276/0x300
[<ffffffff81134a4d>] handle_mm_fault+0x62d/0xba0
[<ffffffff8103e2f1>] __do_page_fault+0x191/0x510
[<ffffffff81030122>] ? native_smp_send_reschedule+0x42/0x60
[<ffffffff8106dc00>] ? check_preempt_curr+0x80/0xa0
[<ffffffff8107092c>] ? wake_up_new_task+0x11c/0x1a0
[<ffffffff8104887d>] ? do_fork+0x14d/0x340
[<ffffffff811799bb>] ? get_unused_fd_flags+0x2b/0x30
[<ffffffff811799df>] ? __fd_install+0x1f/0x60
[<ffffffff8103e67c>] do_page_fault+0xc/0x10
[<ffffffff8150d322>] page_fault+0x22/0x30
RIP [<ffffffff81074191>] task_scan_min+0x21/0x50
RSP <ffff880037a6bce0>
---[ end trace 9a826d16936c04de ]---

Also fix race in task_scan_min (it depends on compiler behaviour).

Signed-off-by: Kirill Tkhai <[email protected]>
---
kernel/sched/fair.c | 5 +++--
kernel/sysctl.c | 3 ++-
2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b78280c..a8dca8e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -828,11 +828,12 @@ static unsigned int task_nr_scan_windows(struct task_struct *p)

static unsigned int task_scan_min(struct task_struct *p)
{
+ unsigned int scan_size = ACCESS_ONCE(sysctl_numa_balancing_scan_size);
unsigned int scan, floor;
unsigned int windows = 1;

- if (sysctl_numa_balancing_scan_size < MAX_SCAN_WINDOW)
- windows = MAX_SCAN_WINDOW / sysctl_numa_balancing_scan_size;
+ if (scan_size < MAX_SCAN_WINDOW)
+ windows = MAX_SCAN_WINDOW / scan_size;
floor = 1000 / windows;

scan = sysctl_numa_balancing_scan_period_min / task_nr_scan_windows(p);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4aada6d..15f2511 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -387,7 +387,8 @@ static struct ctl_table kern_table[] = {
.data = &sysctl_numa_balancing_scan_size,
.maxlen = sizeof(unsigned int),
.mode = 0644,
- .proc_handler = proc_dointvec,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &one,
},
{
.procname = "numa_balancing",



Subject: [tip:sched/core] sched/fair: Fix division by zero sysctl_numa_balancing_scan_size

Commit-ID: 6419265899d9bd27e5ff9f8b43db3715407fc2ba
Gitweb: http://git.kernel.org/tip/6419265899d9bd27e5ff9f8b43db3715407fc2ba
Author: Kirill Tkhai <[email protected]>
AuthorDate: Thu, 16 Oct 2014 14:39:37 +0400
Committer: Ingo Molnar <[email protected]>
CommitDate: Tue, 28 Oct 2014 10:46:04 +0100

sched/fair: Fix division by zero sysctl_numa_balancing_scan_size

File /proc/sys/kernel/numa_balancing_scan_size_mb allows writing of zero.

This bash command reproduces problem:

$ while :; do echo 0 > /proc/sys/kernel/numa_balancing_scan_size_mb; \
echo 256 > /proc/sys/kernel/numa_balancing_scan_size_mb; done

divide error: 0000 [#1] SMP
Modules linked in:
CPU: 0 PID: 24112 Comm: bash Not tainted 3.17.0+ #8
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88013c852600 ti: ffff880037a68000 task.ti: ffff880037a68000
RIP: 0010:[<ffffffff81074191>] [<ffffffff81074191>] task_scan_min+0x21/0x50
RSP: 0000:ffff880037a6bce0 EFLAGS: 00010246
RAX: 0000000000000a00 RBX: 00000000000003e8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88013c852600
RBP: ffff880037a6bcf0 R08: 0000000000000001 R09: 0000000000015c90
R10: ffff880239bf6c00 R11: 0000000000000016 R12: 0000000000003fff
R13: ffff88013c852600 R14: ffffea0008d1b000 R15: 0000000000000003
FS: 00007f12bb048700(0000) GS:ffff88007da00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000001505678 CR3: 0000000234770000 CR4: 00000000000006f0
Stack:
ffff88013c852600 0000000000003fff ffff880037a6bd18 ffffffff810741d1
ffff88013c852600 0000000000003fff 000000000002bfff ffff880037a6bda8
ffffffff81077ef7 ffffea0008a56d40 0000000000000001 0000000000000001
Call Trace:
[<ffffffff810741d1>] task_scan_max+0x11/0x40
[<ffffffff81077ef7>] task_numa_fault+0x1f7/0xae0
[<ffffffff8115a896>] ? migrate_misplaced_page+0x276/0x300
[<ffffffff81134a4d>] handle_mm_fault+0x62d/0xba0
[<ffffffff8103e2f1>] __do_page_fault+0x191/0x510
[<ffffffff81030122>] ? native_smp_send_reschedule+0x42/0x60
[<ffffffff8106dc00>] ? check_preempt_curr+0x80/0xa0
[<ffffffff8107092c>] ? wake_up_new_task+0x11c/0x1a0
[<ffffffff8104887d>] ? do_fork+0x14d/0x340
[<ffffffff811799bb>] ? get_unused_fd_flags+0x2b/0x30
[<ffffffff811799df>] ? __fd_install+0x1f/0x60
[<ffffffff8103e67c>] do_page_fault+0xc/0x10
[<ffffffff8150d322>] page_fault+0x22/0x30
RIP [<ffffffff81074191>] task_scan_min+0x21/0x50
RSP <ffff880037a6bce0>
---[ end trace 9a826d16936c04de ]---

Also fix race in task_scan_min (it depends on compiler behaviour).

Signed-off-by: Kirill Tkhai <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Aaron Tomlin <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Dario Faggioli <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Rik van Riel <[email protected]>
Link: http://lkml.kernel.org/r/1413455977.24793.78.camel@tkhai
Signed-off-by: Ingo Molnar <[email protected]>
---
kernel/sched/fair.c | 5 +++--
kernel/sysctl.c | 3 ++-
2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e9abd4e..34baa60 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -828,11 +828,12 @@ static unsigned int task_nr_scan_windows(struct task_struct *p)

static unsigned int task_scan_min(struct task_struct *p)
{
+ unsigned int scan_size = ACCESS_ONCE(sysctl_numa_balancing_scan_size);
unsigned int scan, floor;
unsigned int windows = 1;

- if (sysctl_numa_balancing_scan_size < MAX_SCAN_WINDOW)
- windows = MAX_SCAN_WINDOW / sysctl_numa_balancing_scan_size;
+ if (scan_size < MAX_SCAN_WINDOW)
+ windows = MAX_SCAN_WINDOW / scan_size;
floor = 1000 / windows;

scan = sysctl_numa_balancing_scan_period_min / task_nr_scan_windows(p);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4aada6d..15f2511 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -387,7 +387,8 @@ static struct ctl_table kern_table[] = {
.data = &sysctl_numa_balancing_scan_size,
.maxlen = sizeof(unsigned int),
.mode = 0644,
- .proc_handler = proc_dointvec,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &one,
},
{
.procname = "numa_balancing",