[Devel] [PATCH RHEL7 COMMIT] ms/mm: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn()

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.17.1.vz7.45.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.17.1.vz7.45.7
------>
commit 54ebe4dfd07d1ecd36fc6bed41704c35a0e08703
Author: Kirill Tkhai <ktkhai at virtuozzo.com>
Date:   Thu Mar 15 15:18:40 2018 +0300

    ms/mm: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn()
    
    In case of memory deficit and low percpu memory pages,
    pcpu_balance_workfn() takes pcpu_alloc_mutex for a long
    time (as it makes memory allocations itself and waits
    for memory reclaim). If tasks doing pcpu_alloc() are
    choosen by OOM killer, they can't exit, because they
    are waiting for the mutex.
    
    The patch makes pcpu_alloc() to care about killing signal
    and use mutex_lock_killable(), when it's allowed by GFP
    flags. This guarantees, a task does not miss SIGKILL
    from OOM killer.
    
    Accepted in ms: https://lkml.org/lkml/2018/3/14/351
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 mm/percpu.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index b15513d4a101..2cac240c015c 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -894,8 +894,12 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
 		return NULL;
 	}
 
-	if (!is_atomic)
-		mutex_lock(&pcpu_alloc_mutex);
+	if (!is_atomic) {
+		if (gfp & __GFP_NOFAIL)
+			mutex_lock(&pcpu_alloc_mutex);
+		else if (mutex_lock_killable(&pcpu_alloc_mutex))
+			return NULL;
+	}
 
 	spin_lock_irqsave(&pcpu_lock, flags);