From: akpm@linux-foundation.org
To: andrii@kernel.org, axboe@kernel.dk, cl@linux.com,
iamjoonsoo.kim@lge.com, ming.lei@redhat.com,
mm-commits@vger.kernel.org, paulmck@kernel.org,
penberg@kernel.org, rientjes@google.com, vbabka@suse.cz
Subject: [merged] percpu_ref-dump-mem_dump_obj-info-upon-reference-count-underflow.patch removed from -mm tree
Date: Thu, 07 Jan 2021 14:32:49 -0800 [thread overview]
Message-ID: <20210107223249.kxVr7w66T%akpm@linux-foundation.org> (raw)
The patch titled
Subject: percpu_ref: dump mem_dump_obj() info upon reference-count underflow
has been removed from the -mm tree. Its filename was
percpu_ref-dump-mem_dump_obj-info-upon-reference-count-underflow.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: "Paul E. McKenney" <paulmck@kernel.org>
Subject: percpu_ref: dump mem_dump_obj() info upon reference-count underflow
Reference-count underflow for percpu_ref is detected in the RCU callback
percpu_ref_switch_to_atomic_rcu(), and the resulting warning does not
print anything allowing easy identification of which percpu_ref use case
is underflowing. This is of course not normally a problem when developing
a new percpu_ref use case because it is most likely that the problem
resides in this new use case. However, when deploying a new kernel to a
large set of servers, the underflow might well be a new corner case in any
of the old percpu_ref use cases.
This commit therefore calls mem_dump_obj() to dump out any additional
available information on the underflowing percpu_ref instance.
Link: https://lkml.kernel.org/r/20210106011750.13709-6-paulmck@kernel.org
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
lib/percpu-refcount.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
--- a/lib/percpu-refcount.c~percpu_ref-dump-mem_dump_obj-info-upon-reference-count-underflow
+++ a/lib/percpu-refcount.c
@@ -5,6 +5,7 @@
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/slab.h>
+#include <linux/mm.h>
#include <linux/percpu-refcount.h>
/*
@@ -168,6 +169,7 @@ static void percpu_ref_switch_to_atomic_
struct percpu_ref_data, rcu);
struct percpu_ref *ref = data->ref;
unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
+ static atomic_t underflows;
unsigned long count = 0;
int cpu;
@@ -191,9 +193,13 @@ static void percpu_ref_switch_to_atomic_
*/
atomic_long_add((long)count - PERCPU_COUNT_BIAS, &data->count);
- WARN_ONCE(atomic_long_read(&data->count) <= 0,
- "percpu ref (%ps) <= 0 (%ld) after switching to atomic",
- data->release, atomic_long_read(&data->count));
+ if (WARN_ONCE(atomic_long_read(&data->count) <= 0,
+ "percpu ref (%ps) <= 0 (%ld) after switching to atomic",
+ data->release, atomic_long_read(&data->count)) &&
+ atomic_inc_return(&underflows) < 4) {
+ pr_err("%s(): percpu_ref underflow", __func__);
+ mem_dump_obj(data);
+ }
/* @ref is viewed as dead on all CPUs, send out switch confirmation */
percpu_ref_call_confirm_rcu(rcu);
_
Patches currently in -mm which might be from paulmck@kernel.org are
reply other threads:[~2021-01-07 22:33 UTC|newest]
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