Srikar Dronamraju reported that the following assert triggers on
his box:
kernel BUG at ../kernel/sched/fair.c:2371!
Call Trace:
[<ffffffff8113cd0e>] __do_numa_page+0xde/0x160
[<ffffffff8113de9e>] handle_pte_fault+0x32e/0xcd0
[<ffffffffa01c22c0>] ? drop_large_spte+0x30/0x30 [kvm]
[<ffffffffa01bf215>] ? kvm_set_spte_hva+0x25/0x30 [kvm]
[<ffffffff8113eab9>] handle_mm_fault+0x279/0x760
[<ffffffff8115c024>] break_ksm+0x74/0xa0
[<ffffffff8115c222>] break_cow+0xa2/0xb0
[<ffffffff8115e38c>] ksm_scan_thread+0xb5c/0xd50
[<ffffffff810771c0>] ? wake_up_bit+0x40/0x40
[<ffffffff8115d830>] ? run_store+0x340/0x340
[<ffffffff8107692e>] kthread+0xce/0xe0
This means that task_numa_fault() was called for a kernel thread
which has no fault tracking.
This scenario is actually possible if a kernel thread does
fault processing on behalf of a user-space task - ignore
the page fault in that case.
Also remove the (now never triggering) assert and robustify
a nearby assert.
Reported-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Andrea Arcangeli <aarca...@redhat.com>
Cc: Rik van Riel <r...@redhat.com>
Cc: Mel Gorman <mgor...@suse.de>
Cc: Hugh Dickins <hu...@google.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
kernel/sched/fair.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9d11a8a..61c7a10 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2351,6 +2351,13 @@ void task_numa_fault(unsigned long addr, int node, int
last_cpupid, int pages, b
int priv;
int idx;
+ /*
+ * Kernel threads might not have an mm but might still
+ * do fault processing (such as KSM):
+ */
+ if (!p->numa_faults)
+ return;
+
if (last_cpupid != cpu_pid_to_cpupid(-1, -1)) {
/* Did we access it last time around? */
if (last_pid == this_pid) {
@@ -2367,8 +2374,8 @@ void task_numa_fault(unsigned long addr, int node, int
last_cpupid, int pages, b
idx = 2*node + priv;
- WARN_ON_ONCE(last_cpu == -1 || node == -1);
- BUG_ON(!p->numa_faults);
+ if (WARN_ON_ONCE(last_cpu == -1 || node == -1))
+ return;
p->numa_faults_curr[idx] += pages;
shared_fault_tick(p, node, last_cpu, pages);
--
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