On Tue, Jul 07, 2015 at 10:27:58PM +0800, kernel test robot wrote:
> Greetings,
>
> 0day kernel testing robot got the below dmesg and the first bad commit is
>
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>
> commit 0e1cc95b4cc7293bb7b39175035e7f7e45c90977
> Author: Mel Gorman <mgorman@xxxxxxx>
> AuthorDate: Tue Jun 30 14:57:27 2015 -0700
> Commit: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> CommitDate: Tue Jun 30 19:44:56 2015 -0700
>
> mm: meminit: finish initialisation of struct pages before basic setup
>
> Waiman Long reported that 24TB machines hit OOM during basic setup when
> struct page initialisation was deferred. One approach is to initialise
> memory on demand but it interferes with page allocator paths. This patch
> creates dedicated threads to initialise memory before basic setup. It
> then blocks on a rw_semaphore until completion as a wait_queue and counter
> is overkill. This may be slower to boot but it's simplier overall and
> also gets rid of a section mangling which existed so kswapd could do the
> initialisation.
>
> [akpm@xxxxxxxxxxxxxxxxxxxx: include rwsem.h, use DECLARE_RWSEM, fix comment, remove unneeded cast]
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> Cc: Waiman Long <waiman.long@xxxxxx
> Cc: Nathan Zimmer <nzimmer@xxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: Scott Norton <scott.norton@xxxxxx>
> Tested-by: Daniel J Blueman <daniel@xxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>
Would it be possible to test with this patch on top?
---8<---
From: Nicolai Stange <nicstange@xxxxxxxxx>
Subject: Re: [PATCH] mm/page_alloc: deferred meminit: replace rwsem with completion
Commit 0e1cc95b4cc7
("mm: meminit: finish initialisation of struct pages before basic setup")
introduced a rwsem to signal completion of the initialization workers.
Lockdep complains about possible recursive locking:
=============================================
[ INFO: possible recursive locking detected ]
4.1.0-12802-g1dc51b8 #3 Not tainted
---------------------------------------------
swapper/0/1 is trying to acquire lock:
(pgdat_init_rwsem){++++.+},
at: [<ffffffff8424c7fb>] page_alloc_init_late+0xc7/0xe6
but task is already holding lock:
(pgdat_init_rwsem){++++.+},
at: [<ffffffff8424c772>] page_alloc_init_late+0x3e/0xe6
Replace the rwsem by a completion together with an atomic
"outstanding work counter".
Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/page_alloc.c | 34 +++++++++++++++++++++++++++-------
1 file changed, 27 insertions(+), 7 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 506eac8..3886e66 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -18,7 +18,9 @@
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/interrupt.h>
-#include <linux/rwsem.h>
+#include <linux/completion.h>
+#include <linux/atomic.h>
+#include <asm/barrier.h>
#include <linux/pagemap.h>
#include <linux/jiffies.h>
#include <linux/bootmem.h>
@@ -1062,7 +1064,20 @@ static void __init deferred_free_range(struct page *page,
__free_pages_boot_core(page, pfn, 0);
}
-static __initdata DECLARE_RWSEM(pgdat_init_rwsem);
+/* counter and completion tracking outstanding deferred_init_memmap()
+ threads */
+static atomic_t pgdat_init_n_undone __initdata;
+static __initdata DECLARE_COMPLETION(pgdat_init_all_done_comp);
+
+static inline void __init pgdat_init_report_one_done(void)
+{
+ /* Write barrier is paired with read barrier in
+ page_alloc_init_late(). It makes all writes visible to
+ readers seeing our decrement on pgdat_init_n_undone. */
+ smp_wmb();
+ if (atomic_dec_and_test(&pgdat_init_n_undone))
+ complete(&pgdat_init_all_done_comp);
+}
/* Initialise remaining memory on a node */
static int __init deferred_init_memmap(void *data)
@@ -1079,7 +1094,7 @@ static int __init deferred_init_memmap(void *data)
const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
if (first_init_pfn == ULONG_MAX) {
- up_read(&pgdat_init_rwsem);
+ pgdat_init_report_one_done();
return 0;
}
@@ -1179,7 +1194,8 @@ free_range:
pr_info("node %d initialised, %lu pages in %ums\n", nid, nr_pages,
jiffies_to_msecs(jiffies - start));
- up_read(&pgdat_init_rwsem);
+
+ pgdat_init_report_one_done();
return 0;
}
@@ -1187,14 +1203,18 @@ void __init page_alloc_init_late(void)
{
int nid;
+ /* There will be num_node_state(N_MEMORY) threads */
+ atomic_set(&pgdat_init_n_undone, num_node_state(N_MEMORY));
for_each_node_state(nid, N_MEMORY) {
- down_read(&pgdat_init_rwsem);
kthread_run(deferred_init_memmap, NODE_DATA(nid), "pgdatinit%d", nid);
}
/* Block until all are initialised */
- down_write(&pgdat_init_rwsem);
- up_write(&pgdat_init_rwsem);
+ wait_for_completion(&pgdat_init_all_done_comp);
+
+ /* Paired with write barrier in deferred_init_memmap(),
+ ensures a consistent view of all its writes. */
+ smp_rmb();
}
#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
--
2.4.5
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