@@ -1035,8 +1035,6 @@ static void task_numa_assign(struct task_numa_env *env,
{
if (env->best_task)
put_task_struct(env->best_task);
- if (p)
- get_task_struct(p);
env->best_task = p;
env->best_imp = imp;
@@ -1058,20 +1056,30 @@ static void task_numa_compare(struct task_numa_env *env,
long dst_load, src_load;
long load;
long imp = (groupimp > 0) ? groupimp : taskimp;
+ bool assigned = false;
rcu_read_lock();
raw_spin_lock_irq(&dst_rq->lock);
cur = dst_rq->curr;
/*
- * No need to move the exiting task, and this ensures that ->curr
- * wasn't reaped and thus get_task_struct() in task_numa_assign()
- * is safe under RCU read lock.
- * Note that rcu_read_lock() itself can't protect from the final
- * put_task_struct() after the last schedule().
+ * No need to move the exiting task or idle task.
*/
if ((cur->flags & PF_EXITING) || is_idle_task(cur))
cur = NULL;
+ else {
+ /*
+ * The task_struct must be protected here to protect the
+ * p->numa_faults access in the task_weight since the
+ * numa_faults could already be freed in the following path:
+ * finish_task_switch()
+ * --> put_task_struct()
+ * --> __put_task_struct()
+ * --> task_numa_free()
+ */
+ get_task_struct(cur);
+ }
+
raw_spin_unlock_irq(&dst_rq->lock);
/*
@@ -1161,8 +1169,15 @@ balance:
goto unlock;
assign:
+ assigned = true;
task_numa_assign(env, cur, imp);
unlock:
+ /*
+ * The dst_rq->curr isn't assigned. The protection for task_struct is
+ * finished.
+ */
+ if (cur && !assigned)
+ put_task_struct(cur);
rcu_read_unlock();
}
BugLink: https://bugs.launchpad.net/bugs/1527643 The following message can be observed on the Ubuntu v3.13.0-65 with KASan backported: ================================================================== BUG: KASan: use after free in task_numa_find_cpu+0x64c/0x890 at addr ffff880dd393ecd8 Read of size 8 by task qemu-system-x86/3998900 ============================================================================= BUG kmalloc-128 (Tainted: G B ): kasan: bad access detected ----------------------------------------------------------------------------- INFO: Allocated in task_numa_fault+0xc1b/0xed0 age=41980 cpu=18 pid=3998890 __slab_alloc+0x4f8/0x560 __kmalloc+0x1eb/0x280 task_numa_fault+0xc1b/0xed0 do_numa_page+0x192/0x200 handle_mm_fault+0x808/0x1160 __do_page_fault+0x218/0x750 do_page_fault+0x1a/0x70 page_fault+0x28/0x30 SyS_poll+0x66/0x1a0 system_call_fastpath+0x1a/0x1f INFO: Freed in task_numa_free+0x1d2/0x200 age=62 cpu=18 pid=0 __slab_free+0x2ab/0x3f0 kfree+0x161/0x170 task_numa_free+0x1d2/0x200 finish_task_switch+0x1d2/0x210 __schedule+0x5d4/0xc60 schedule_preempt_disabled+0x40/0xc0 cpu_startup_entry+0x2da/0x340 start_secondary+0x28f/0x360 Call Trace: [<ffffffff81a6ce35>] dump_stack+0x45/0x56 [<ffffffff81244aed>] print_trailer+0xfd/0x170 [<ffffffff8124ac36>] object_err+0x36/0x40 [<ffffffff8124cbf9>] kasan_report_error+0x1e9/0x3a0 [<ffffffff8124d260>] kasan_report+0x40/0x50 [<ffffffff810dda7c>] ? task_numa_find_cpu+0x64c/0x890 [<ffffffff8124bee9>] __asan_load8+0x69/0xa0 [<ffffffff814f5c38>] ? find_next_bit+0xd8/0x120 [<ffffffff810dda7c>] task_numa_find_cpu+0x64c/0x890 [<ffffffff810de16c>] task_numa_migrate+0x4ac/0x7b0 [<ffffffff810de523>] numa_migrate_preferred+0xb3/0xc0 [<ffffffff810e0b88>] task_numa_fault+0xb88/0xed0 [<ffffffff8120ef02>] do_numa_page+0x192/0x200 [<ffffffff81211038>] handle_mm_fault+0x808/0x1160 [<ffffffff810d7dbd>] ? sched_clock_cpu+0x10d/0x160 [<ffffffff81068c52>] ? native_load_tls+0x82/0xa0 [<ffffffff81a7bd68>] __do_page_fault+0x218/0x750 [<ffffffff810c2186>] ? hrtimer_try_to_cancel+0x76/0x160 [<ffffffff81a6f5e7>] ? schedule_hrtimeout_range_clock.part.24+0xf7/0x1c0 [<ffffffff81a7c2ba>] do_page_fault+0x1a/0x70 [<ffffffff81a772e8>] page_fault+0x28/0x30 [<ffffffff8128cbd4>] ? do_sys_poll+0x1c4/0x6d0 [<ffffffff810e64f6>] ? enqueue_task_fair+0x4b6/0xaa0 [<ffffffff810233c9>] ? sched_clock+0x9/0x10 [<ffffffff810cf70a>] ? resched_task+0x7a/0xc0 [<ffffffff810d0663>] ? check_preempt_curr+0xb3/0x130 [<ffffffff8128b5c0>] ? poll_select_copy_remaining+0x170/0x170 [<ffffffff810d3bc0>] ? wake_up_state+0x10/0x20 [<ffffffff8112a28f>] ? drop_futex_key_refs.isra.14+0x1f/0x90 [<ffffffff8112d40e>] ? futex_requeue+0x3de/0xba0 [<ffffffff8112e49e>] ? do_futex+0xbe/0x8f0 [<ffffffff81022c89>] ? read_tsc+0x9/0x20 [<ffffffff8111bd9d>] ? ktime_get_ts+0x12d/0x170 [<ffffffff8108f699>] ? timespec_add_safe+0x59/0xe0 [<ffffffff8128d1f6>] SyS_poll+0x66/0x1a0 [<ffffffff81a830dd>] system_call_fastpath+0x1a/0x1f As commit 1effd9f19324 ("sched/numa: Fix unsafe get_task_struct() in task_numa_assign()") points out, the rcu_read_lock() cannot protect the task_struct from being freed in the finish_task_switch(). And the bug happens in the process of calculation of imp which requires the access of p->numa_faults being freed in the following path: do_exit() current->flags |= PF_EXITING; release_task() ~~delayed_put_task_struct()~~ schedule() ... ... rq->curr = next; context_switch() finish_task_switch() put_task_struct() __put_task_struct() task_numa_free() The fix here to get_task_struct() early before end of dst_rq->lock to protect the calculation process and also put_task_struct() in the corresponding point if finally the dst_rq->curr somehow cannot be assigned. Additional credit to Liang Chen who helped fix the error logic and add the put_task_struct() to the place it missed. Signed-off-by: Gavin Guo <gavin.guo@canonical.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Hugh Dickins <hughd@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: jay.vosburgh@canonical.com Cc: liang.chen@canonical.com Link: http://lkml.kernel.org/r/1453264618-17645-1-git-send-email-gavin.guo@canonical.com Signed-off-by: Ingo Molnar <mingo@kernel.org> (backported from commit 1dff76b92f69051e579bdc131e01500da9fa2a91) Signed-off-by: Gavin Guo <gavin.guo@canonical.com> Conflicts: kernel/sched/fair.c --- kernel/sched/fair.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-)