The patch titled
Subject: mm, meminit: replace rwsem with completion
has been added to the -mm tree. Its filename is
mm-meminit-replace-rwsem-with-completion.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-meminit-replace-rwsem-with-completion.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-meminit-replace-rwsem-with-completion.patch
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------------------------------------------------------
From: Nicolai Stange <nicstange@xxxxxxxxx>
Subject: mm, 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".
[peterz@xxxxxxxxxxxxx: Barrier removal on the grounds of being pointless]
[mgorman@xxxxxxx: Applied review feedback]
Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Alex Ng <alexng@xxxxxxxxxxxxx>
Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 22 +++++++++++++++-------
1 file changed, 15 insertions(+), 7 deletions(-)
diff -puN mm/page_alloc.c~mm-meminit-replace-rwsem-with-completion mm/page_alloc.c
--- a/mm/page_alloc.c~mm-meminit-replace-rwsem-with-completion
+++ a/mm/page_alloc.c
@@ -18,7 +18,6 @@
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/interrupt.h>
-#include <linux/rwsem.h>
#include <linux/pagemap.h>
#include <linux/jiffies.h>
#include <linux/bootmem.h>
@@ -1060,7 +1059,15 @@ static void __init deferred_free_range(s
__free_pages_boot_core(page, pfn, 0);
}
-static __initdata DECLARE_RWSEM(pgdat_init_rwsem);
+/* Completion tracking for 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)
+{
+ 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)
@@ -1077,7 +1084,7 @@ static int __init deferred_init_memmap(v
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;
}
@@ -1177,7 +1184,8 @@ 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;
}
@@ -1185,14 +1193,14 @@ 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);
}
#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
_
Patches currently in -mm which might be from nicstange@xxxxxxxxx are
mm-meminit-allow-early_pfn_to_nid-to-be-used-during-runtime.patch
mm-meminit-replace-rwsem-with-completion.patch
fs-file-table-reinit-files_statmax_files-after-deferred-memory-initialisation.patch
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