• Kirill Tkhai's avatar
    sched/fair: Fix division by zero sysctl_numa_balancing_scan_size · 64192658
    Kirill Tkhai authored
    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: default avatarKirill Tkhai <ktkhai@parallels.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Aaron Tomlin <atomlin@redhat.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Dario Faggioli <raistlin@linux.it>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Jens Axboe <axboe@fb.com>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Rik van Riel <riel@redhat.com>
    Link: http://lkml.kernel.org/r/1413455977.24793.78.camel@tkhaiSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    64192658
fair.c 206 KB