OOM killed tasks have access to memory reserves as specified by the
TIF_MEMDIE flag in the hopes that it will quickly exit. If such a task
has memory allocations constrained by cpusets, we may encounter a
deadlock if a blocking task cannot exit because it cannot allocate the
necessary memory.
We allow tasks that have the TIF_MEMDIE flag to allocate memory anywhere,
including outside its cpuset restriction, so that it can quickly die
regardless of whether it is __GFP_HARDWALL.
Cc: Andi Kleen <[email protected]>
Cc: Paul Jackson <[email protected]>
Cc: Christoph Lameter <[email protected]>
Signed-off-by: David Rientjes <[email protected]>
---
kernel/cpuset.c | 22 ++++++++++++++++++++--
1 files changed, 20 insertions(+), 2 deletions(-)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2351,6 +2351,8 @@ static const struct cpuset *nearest_exclusive_ancestor(const struct cpuset *cs)
* z's node is in our tasks mems_allowed, yes. If it's not a
* __GFP_HARDWALL request and this zone's nodes is in the nearest
* mem_exclusive cpuset ancestor to this tasks cpuset, yes.
+ * If the task has been OOM killed and has access to memory reserves
+ * as specified by the TIF_MEMDIE flag, yes.
* Otherwise, no.
*
* If __GFP_HARDWALL is set, cpuset_zone_allowed_softwall()
@@ -2368,7 +2370,8 @@ static const struct cpuset *nearest_exclusive_ancestor(const struct cpuset *cs)
* calls get to this routine, we should just shut up and say 'yes'.
*
* GFP_USER allocations are marked with the __GFP_HARDWALL bit,
- * and do not allow allocations outside the current tasks cpuset.
+ * and do not allow allocations outside the current tasks cpuset
+ * unless the task has been OOM killed as is marked TIF_MEMDIE.
* GFP_KERNEL allocations are not so marked, so can escape to the
* nearest enclosing mem_exclusive ancestor cpuset.
*
@@ -2392,6 +2395,7 @@ static const struct cpuset *nearest_exclusive_ancestor(const struct cpuset *cs)
* affect that:
* in_interrupt - any node ok (current task context irrelevant)
* GFP_ATOMIC - any node ok
+ * TIF_MEMDIE - any node ok
* GFP_KERNEL - any node in enclosing mem_exclusive cpuset ok
* GFP_USER - only nodes in current tasks mems allowed ok.
*
@@ -2413,6 +2417,12 @@ int __cpuset_zone_allowed_softwall(struct zone *z, gfp_t gfp_mask)
might_sleep_if(!(gfp_mask & __GFP_HARDWALL));
if (node_isset(node, current->mems_allowed))
return 1;
+ /*
+ * Allow tasks that have access to memory reserves because they have
+ * been OOM killed to get memory anywhere.
+ */
+ if (unlikely(test_thread_flag(TIF_MEMDIE)))
+ return 1;
if (gfp_mask & __GFP_HARDWALL) /* If hardwall request, stop here */
return 0;
@@ -2438,7 +2448,9 @@ int __cpuset_zone_allowed_softwall(struct zone *z, gfp_t gfp_mask)
*
* If we're in interrupt, yes, we can always allocate.
* If __GFP_THISNODE is set, yes, we can always allocate. If zone
- * z's node is in our tasks mems_allowed, yes. Otherwise, no.
+ * z's node is in our tasks mems_allowed, yes. If the task has been
+ * OOM killed and has access to memory reserves as specified by the
+ * TIF_MEMDIE flag, yes. Otherwise, no.
*
* The __GFP_THISNODE placement logic is really handled elsewhere,
* by forcibly using a zonelist starting at a specified node, and by
@@ -2462,6 +2474,12 @@ int __cpuset_zone_allowed_hardwall(struct zone *z, gfp_t gfp_mask)
node = zone_to_nid(z);
if (node_isset(node, current->mems_allowed))
return 1;
+ /*
+ * Allow tasks that have access to memory reserves because they have
+ * been OOM killed to get memory anywhere.
+ */
+ if (unlikely(test_thread_flag(TIF_MEMDIE)))
+ return 1;
return 0;
}
-
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