From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Subject: mm: add private lock to serialize memory hotplug operations
Commit bfc8c90139eb ("mem-hotplug: implement get/put_online_mems")
introduced new functions get/put_online_mems() and mem_hotplug_begin/end()
in order to allow similar semantics for memory hotplug like for cpu
hotplug.
The corresponding functions for cpu hotplug are get/put_online_cpus() and
cpu_hotplug_begin/done() for cpu hotplug.
The commit however missed to introduce functions that would serialize
memory hotplug operations like they are done for cpu hotplug with
cpu_maps_update_begin/done().
This basically leaves mem_hotplug.active_writer unprotected and allows
concurrent writers to modify it, which may lead to problems as outlined by
commit f931ab479dd2 ("mm: fix devm_memremap_pages crash, use
mem_hotplug_{begin, done}").
That commit was extended again with commit b5d24fda9c3d ("mm,
devm_memremap_pages: hold device_hotplug lock over mem_hotplug_{begin,
done}") which serializes memory hotplug operations for some call sites by
using the device_hotplug lock.
In addition with commit 3fc21924100b ("mm: validate device_hotplug is held
for memory hotplug") a sanity check was added to mem_hotplug_begin() to
verify that the device_hotplug lock is held.
This in turn triggers the following warning on s390:
WARNING: CPU: 6 PID: 1 at drivers/base/core.c:643 assert_held_device_hotplug+0x4a/0x58
Call Trace:
assert_held_device_hotplug+0x40/0x58)
mem_hotplug_begin+0x34/0xc8
add_memory_resource+0x7e/0x1f8
add_memory+0xda/0x130
add_memory_merged+0x15c/0x178
sclp_detect_standby_memory+0x2ae/0x2f8
do_one_initcall+0xa2/0x150
kernel_init_freeable+0x228/0x2d8
kernel_init+0x2a/0x140
kernel_thread_starter+0x6/0xc
One possible fix would be to add more lock_device_hotplug() and
unlock_device_hotplug() calls around each call site of
mem_hotplug_begin/end(). But that would give the device_hotplug lock
additional semantics it better should not have (serialize memory hotplug
operations).
Instead add a new memory_add_remove_lock which has the similar semantics
like cpu_add_remove_lock for cpu hotplug.
To keep things hopefully a bit easier the lock will be locked and unlocked
within the mem_hotplug_begin/end() functions.
Link: http://lkml.kernel.org/r/20170314125226.16779-2-heiko.carstens@xxxxxxxxxx
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Reported-by: Sebastian Ott <sebott@xxxxxxxxxxxxxxxxxx>
Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/memremap.c | 4 ----
mm/memory_hotplug.c | 6 +++++-
2 files changed, 5 insertions(+), 5 deletions(-)
diff -puN kernel/memremap.c~mm-add-private-lock-to-serialize-memory-hotplug-operations kernel/memremap.c
--- a/kernel/memremap.c~mm-add-private-lock-to-serialize-memory-hotplug-operations
+++ a/kernel/memremap.c
@@ -247,11 +247,9 @@ static void devm_memremap_pages_release(
align_start = res->start & ~(SECTION_SIZE - 1);
align_size = ALIGN(resource_size(res), SECTION_SIZE);
- lock_device_hotplug();
mem_hotplug_begin();
arch_remove_memory(align_start, align_size);
mem_hotplug_done();
- unlock_device_hotplug();
untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
pgmap_radix_release(res);
@@ -364,11 +362,9 @@ void *devm_memremap_pages(struct device
if (error)
goto err_pfn_remap;
- lock_device_hotplug();
mem_hotplug_begin();
error = arch_add_memory(nid, align_start, align_size, true);
mem_hotplug_done();
- unlock_device_hotplug();
if (error)
goto err_add_memory;
diff -puN mm/memory_hotplug.c~mm-add-private-lock-to-serialize-memory-hotplug-operations mm/memory_hotplug.c
--- a/mm/memory_hotplug.c~mm-add-private-lock-to-serialize-memory-hotplug-operations
+++ a/mm/memory_hotplug.c
@@ -125,9 +125,12 @@ void put_online_mems(void)
}
+/* Serializes write accesses to mem_hotplug.active_writer. */
+static DEFINE_MUTEX(memory_add_remove_lock);
+
void mem_hotplug_begin(void)
{
- assert_held_device_hotplug();
+ mutex_lock(&memory_add_remove_lock);
mem_hotplug.active_writer = current;
@@ -147,6 +150,7 @@ void mem_hotplug_done(void)
mem_hotplug.active_writer = NULL;
mutex_unlock(&mem_hotplug.lock);
memhp_lock_release();
+ mutex_unlock(&memory_add_remove_lock);
}
/* add this memory to iomem resource */
_
--
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