[ Patches inline below for people to comment on ]
On Thu, Dec 19, 2013 at 08:00:42PM -0500, Dave Jones wrote:
> On Thu, Dec 19, 2013 at 06:38:54PM -0500, Benjamin LaHaise wrote:
> > On Thu, Dec 19, 2013 at 03:24:16PM -0500, Dave Jones wrote:
> > > Yes. Note the original trace in this thread was a
> VM_BUG_ON(atomic_read(&page->_count) <= 0);
> > >
> > > Right after these crashes btw, the box locks up solid. So bad that
> traces don't
> > > always make it over usb-serial. Annoying.
> >
> > I think I finally have an idea what's going on now. Kent's changes in
> > e34ecee2ae791df674dfb466ce40692ca6218e43 are broken and result in a memory
> > leak of the aio kioctx. This eventually leads to the system running out
> of
> > memory, which ends up triggering the otherwise hard to hit error paths in
> > aio_setup_ring(). Linus' suggested changes should fix the badness in the
> > aio_setup_ring(), but more work has to be done to fix up the percpu
> > reference counting tie in with the aio code. I'll fix this up in the
> > morning if nobody beats me to it over night, as I'm just heading out right
> > now.
>
> That would explain why I'm having difficulty repeating it in a hurry if it
> takes hours of runtime for the leak to reach a point where it becomes a
> problem.
Okay, I've put the below two patches plus Linus's change through a round
of tests, and it passes millions of iterations of the aio numa migratepage
test, as well as a number of repetitions of a few simple read and write
tests. The first patch fixes the memory leak Kent introduced, while the
second patch makes aio_migratepage() much more paranoid and robust. Those
two changes are in git://git.kvack.org/~bcrl/aio-next.git -- can a few
other folks please review to make sure I haven't missed anything?
Linus, feel free to add my Signed-off-by: to your sanitization of
aio_setup_ring() as well, as it works okay in my testing.
-ben
--
"Thought is the essence of where you are now."
aio.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
commit 1881686f842065d2f92ec9c6424830ffc17d23b0
Author: Benjamin LaHaise <b...@kvack.org>
Date: Sat Dec 21 15:49:28 2013 -0500
aio: fix kioctx leak introduced by "aio: Fix a trinity splat"
e34ecee2ae791df674dfb466ce40692ca6218e43 reworked the percpu reference
counting to correct a bug trinity found. Unfortunately, the change lead
to kioctxes being leaked because there was no final reference count to
put. Add that reference count back in to fix things.
Signed-off-by: Benjamin LaHaise <b...@kvack.org>
Cc: sta...@vger.kernel.org
diff --git a/fs/aio.c b/fs/aio.c
index 6efb7f6..fd1c0ba 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -652,7 +652,8 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
aio_nr += ctx->max_reqs;
spin_unlock(&aio_nr_lock);
- percpu_ref_get(&ctx->users); /* io_setup() will drop this ref */
+ percpu_ref_get(&ctx->users); /* io_setup() will drop this ref */
+ percpu_ref_get(&ctx->reqs); /* free_ioctx_users() will drop this */
err = ioctx_add_table(ctx, mm);
if (err)
fs/aio.c | 52 ++++++++++++++++++++++++++++++++++++++++--------
include/linux/migrate.h | 3 +-
mm/migrate.c | 13 ++++++------
3 files changed, 53 insertions(+), 15 deletions(-)
commit 8e321fefb0e60bae4e2a28d20fc4fa30758d27c6
Author: Benjamin LaHaise <b...@kvack.org>
Date: Sat Dec 21 17:56:08 2013 -0500
aio/migratepages: make aio migrate pages sane
The arbitrary restriction on page counts offered by the core
migrate_page_move_mapping() code results in rather suspicious looking
fiddling with page reference counts in the aio_migratepage() operation.
To fix this, make migrate_page_move_mapping() take an extra_count parameter
that allows aio to tell the code about its own reference count on the page
being migrated.
While cleaning up aio_migratepage(), make it validate that the old page
being passed in is actually what aio_migratepage() expects to prevent
misbehaviour in the case of races.
Signed-off-by: Benjamin LaHaise <b...@kvack.org>
diff --git a/fs/aio.c b/fs/aio.c
index fd1c0ba..efa708b 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -244,9 +244,14 @@ static void aio_free_ring(struct kioctx *ctx)
int i;
for (i = 0; i < ctx->nr_pages; i++) {
+ struct page *page;
pr_debug("pid(%d) [%d] page->count=%d\n", current->pid, i,
page_count(ctx->ring_pages[i]));
- put_page(ctx->ring_pages[i]);
+ page = ctx->ring_pages[i];
+ if (!page)
+ continue;
+ ctx->ring_pages[i] = NULL;
+ put_page(page);
}
put_aio_ring_file(ctx);
@@ -280,18 +285,38 @@ static int aio_migratepage(struct address_space *mapping,
struct page *new,
unsigned long flags;
int rc;
+ rc = 0;
+
+ /* Make sure the old page hasn't already been changed */
+ spin_lock(&mapping->private_lock);
+ ctx = mapping->private_data;
+ if (ctx) {
+ pgoff_t idx;
+ spin_lock_irqsave(&ctx->completion_lock, flags);
+ idx = old->index;
+ if (idx < (pgoff_t)ctx->nr_pages) {
+ if (ctx->ring_pages[idx] != old)
+ rc = -EAGAIN;
+ } else
+ rc = -EINVAL;
+ spin_unlock_irqrestore(&ctx->completion_lock, flags);
+ } else
+ rc = -EINVAL;
+ spin_unlock(&mapping->private_lock);
+
+ if (rc != 0)
+ return rc;
+
/* Writeback must be complete */
BUG_ON(PageWriteback(old));
- put_page(old);
+ get_page(new);
- rc = migrate_page_move_mapping(mapping, new, old, NULL, mode);
+ rc = migrate_page_move_mapping(mapping, new, old, NULL, mode, 1);
if (rc != MIGRATEPAGE_SUCCESS) {
- get_page(old);
+ put_page(new);
return rc;
}
- get_page(new);
-
/* We can potentially race against kioctx teardown here. Use the
* address_space's private data lock to protect the mapping's
* private_data.
@@ -303,13 +328,24 @@ static int aio_migratepage(struct address_space *mapping,
struct page *new,
spin_lock_irqsave(&ctx->completion_lock, flags);
migrate_page_copy(new, old);
idx = old->index;
- if (idx < (pgoff_t)ctx->nr_pages)
- ctx->ring_pages[idx] = new;
+ if (idx < (pgoff_t)ctx->nr_pages) {
+ /* And only do the move if things haven't changed */
+ if (ctx->ring_pages[idx] == old)
+ ctx->ring_pages[idx] = new;
+ else
+ rc = -EAGAIN;
+ } else
+ rc = -EINVAL;
spin_unlock_irqrestore(&ctx->completion_lock, flags);
} else
rc = -EBUSY;
spin_unlock(&mapping->private_lock);
+ if (rc == MIGRATEPAGE_SUCCESS)
+ put_page(old);
+ else
+ put_page(new);
+
return rc;
}
#endif
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index b7717d7..f015c05 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -55,7 +55,8 @@ extern int migrate_huge_page_move_mapping(struct
address_space *mapping,
struct page *newpage, struct page *page);
extern int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page,
- struct buffer_head *head, enum migrate_mode mode);
+ struct buffer_head *head, enum migrate_mode mode,
+ int extra_count);
#else
static inline void putback_lru_pages(struct list_head *l) {}
diff --git a/mm/migrate.c b/mm/migrate.c
index e9b7102..9194375 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -317,14 +317,15 @@ static inline bool buffer_migrate_lock_buffers(struct
buffer_head *head,
*/
int migrate_page_move_mapping(struct address_space *mapping,
struct page *newpage, struct page *page,
- struct buffer_head *head, enum migrate_mode mode)
+ struct buffer_head *head, enum migrate_mode mode,
+ int extra_count)
{
- int expected_count = 0;
+ int expected_count = 1 + extra_count;
void **pslot;
if (!mapping) {
/* Anonymous page without mapping */
- if (page_count(page) != 1)
+ if (page_count(page) != expected_count)
return -EAGAIN;
return MIGRATEPAGE_SUCCESS;
}
@@ -334,7 +335,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
pslot = radix_tree_lookup_slot(&mapping->page_tree,
page_index(page));
- expected_count = 2 + page_has_private(page);
+ expected_count += 1 + page_has_private(page);
if (page_count(page) != expected_count ||
radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) !=
page) {
spin_unlock_irq(&mapping->tree_lock);
@@ -584,7 +585,7 @@ int migrate_page(struct address_space *mapping,
BUG_ON(PageWriteback(page)); /* Writeback must be complete */
- rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode);
+ rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
if (rc != MIGRATEPAGE_SUCCESS)
return rc;
@@ -611,7 +612,7 @@ int buffer_migrate_page(struct address_space *mapping,
head = page_buffers(page);
- rc = migrate_page_move_mapping(mapping, newpage, page, head, mode);
+ rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
if (rc != MIGRATEPAGE_SUCCESS)
return rc;
--
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