lkml.org 
[lkml]   [2020]   [Jan]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH -next v2] mm/hotplug: silence a lockdep splat with printk()
Date
It is guaranteed to trigger a lockdep splat if calling printk() with
zone->lock held because there are many places (tty, console drivers,
debugobjects etc) would allocate some memory with another lock
held which is proved to be difficult to fix them all.

A common workaround until the onging effort to make all printk() as
deferred happens is to use printk_deferred() in those places similar to
the recent commit [1] merged into the random and -next trees, but memory
offline will call dump_page() which needs to be deferred after the lock.

So change has_unmovable_pages() so that it no longer calls dump_page()
itself - instead it returns a "struct page *" of the unmovable page back
to the caller so that in the case of a has_unmovable_pages() failure,
the caller can call dump_page() after releasing zone->lock. Also, make
dump_page() is able to report a CMA page as well, so the reason string
from has_unmovable_pages() can be removed.

While at it, remove a similar but unnecessary debug-only printk() as
well.

[1] https://lore.kernel.org/lkml/1573679785-21068-1-git-send-email-cai@lca.pw/

Signed-off-by: Qian Cai <cai@lca.pw>
---

v2: Improve the commit log and report CMA in dump_page() per Andrew.
has_unmovable_pages() returns a "struct page *" to the caller.

include/linux/page-isolation.h | 4 ++--
mm/debug.c | 5 +++--
mm/memory_hotplug.c | 6 ++++--
mm/page_alloc.c | 18 +++++-------------
mm/page_isolation.c | 7 ++++++-
5 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 148e65a9c606..da043ae86488 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -33,8 +33,8 @@ static inline bool is_migrate_isolate(int migratetype)
#define MEMORY_OFFLINE 0x1
#define REPORT_FAILURE 0x2

-bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype,
- int flags);
+struct page *has_unmovable_pages(struct zone *zone, struct page *page, int
+ migratetype, int flags);
void set_pageblock_migratetype(struct page *page, int migratetype);
int move_freepages_block(struct zone *zone, struct page *page,
int migratetype, int *num_movable);
diff --git a/mm/debug.c b/mm/debug.c
index 0461df1207cb..2165a4c83b97 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -46,6 +46,7 @@ void __dump_page(struct page *page, const char *reason)
{
struct address_space *mapping;
bool page_poisoned = PagePoisoned(page);
+ bool page_cma = is_migrate_cma_page(page);
int mapcount;

/*
@@ -74,9 +75,9 @@ void __dump_page(struct page *page, const char *reason)
page->mapping, page_to_pgoff(page),
compound_mapcount(page));
else
- pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n",
+ pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx cma:%d\n",
page, page_ref_count(page), mapcount,
- page->mapping, page_to_pgoff(page));
+ page->mapping, page_to_pgoff(page), page_cma);
if (PageKsm(page))
pr_warn("ksm flags: %#lx(%pGp)\n", page->flags, &page->flags);
else if (PageAnon(page))
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 7a6de9b0dcab..06e7dd3eb9a9 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1148,8 +1148,10 @@ static bool is_pageblock_removable_nolock(unsigned long pfn)
if (!zone_spans_pfn(zone, pfn))
return false;

- return !has_unmovable_pages(zone, page, MIGRATE_MOVABLE,
- MEMORY_OFFLINE);
+ if (has_unmovable_pages(zone, page, MIGRATE_MOVABLE, MEMORY_OFFLINE))
+ return false;
+
+ return true;
}

/* Checks if this range of memory is likely to be hot-removable. */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e56cd1f33242..728e36f24aea 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8203,12 +8203,11 @@ void *__init alloc_large_system_hash(const char *tablename,
* check without lock_page also may miss some movable non-lru pages at
* race condition. So you can't expect this function should be exact.
*/
-bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype,
- int flags)
+struct page *has_unmovable_pages(struct zone *zone, struct page *page,
+ int migratetype, int flags)
{
unsigned long iter = 0;
unsigned long pfn = page_to_pfn(page);
- const char *reason = "unmovable page";

/*
* TODO we could make this much more efficient by not checking every
@@ -8225,9 +8224,8 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype,
* so consider them movable here.
*/
if (is_migrate_cma(migratetype))
- return false;
+ return NULL;

- reason = "CMA page";
goto unmovable;
}

@@ -8302,12 +8300,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype,
*/
goto unmovable;
}
- return false;
+ return NULL;
unmovable:
WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
- if (flags & REPORT_FAILURE)
- dump_page(pfn_to_page(pfn + iter), reason);
- return true;
+ return pfn_to_page(pfn + iter);
}

#ifdef CONFIG_CONTIG_ALLOC
@@ -8711,10 +8707,6 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
BUG_ON(!PageBuddy(page));
order = page_order(page);
offlined_pages += 1 << order;
-#ifdef CONFIG_DEBUG_VM
- pr_info("remove from free list %lx %d %lx\n",
- pfn, 1 << order, end_pfn);
-#endif
del_page_from_free_area(page, &zone->free_area[order]);
pfn += (1 << order);
}
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 1f8b9dfecbe8..a2b730ea3732 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -20,6 +20,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
struct zone *zone;
unsigned long flags;
int ret = -EBUSY;
+ struct page *unmovable = NULL;

zone = page_zone(page);

@@ -37,7 +38,8 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
* FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
* We just check MOVABLE pages.
*/
- if (!has_unmovable_pages(zone, page, migratetype, isol_flags)) {
+ unmovable = has_unmovable_pages(zone, page, migratetype, isol_flags);
+ if (!unmovable) {
unsigned long nr_pages;
int mt = get_pageblock_migratetype(page);

@@ -54,6 +56,9 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
spin_unlock_irqrestore(&zone->lock, flags);
if (!ret)
drain_all_pages(zone);
+ else if (isol_flags & REPORT_FAILURE && unmovable)
+ dump_page(unmovable, "unmovable page");
+
return ret;
}

--
2.21.0 (Apple Git-122.2)
\
 
 \ /
  Last update: 2020-01-15 06:32    [W:0.070 / U:14.252 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site