Syzbot is reporting potential deadlocks due to pagesets.lock when
PAGE_OWNER is enabled. One example from Desmond Cheong Zhi Xi is
as follows
__alloc_pages_bulk()
local_lock_irqsave(&pagesets.lock, flags) <---- outer lock here
prep_new_page():
post_alloc_hook():
set_page_owner():
__set_page_owner():
save_stack():
stack_depot_save():
alloc_pages():
alloc_page_interleave():
__alloc_pages():
get_page_from_freelist():
rm_queue():
rm_queue_pcplist():
local_lock_irqsave(&pagesets.lock, flags);
*** DEADLOCK ***
Zhang, Qiang also reported
BUG: sleeping function called from invalid context at mm/page_alloc.c:5179
in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 1, name: swapper/0
.....
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:96
___might_sleep.cold+0x1f1/0x237 kernel/sched/core.c:9153
prepare_alloc_pages+0x3da/0x580 mm/page_alloc.c:5179
__alloc_pages+0x12f/0x500 mm/page_alloc.c:5375
alloc_page_interleave+0x1e/0x200 mm/mempolicy.c:2147
alloc_pages+0x238/0x2a0 mm/mempolicy.c:2270
stack_depot_save+0x39d/0x4e0 lib/stackdepot.c:303
save_stack+0x15e/0x1e0 mm/page_owner.c:120
__set_page_owner+0x50/0x290 mm/page_owner.c:181
prep_new_page mm/page_alloc.c:2445 [inline]
__alloc_pages_bulk+0x8b9/0x1870 mm/page_alloc.c:5313
alloc_pages_bulk_array_node include/linux/gfp.h:557 [inline]
vm_area_alloc_pages mm/vmalloc.c:2775 [inline]
__vmalloc_area_node mm/vmalloc.c:2845 [inline]
__vmalloc_node_range+0x39d/0x960 mm/vmalloc.c:2947
__vmalloc_node mm/vmalloc.c:2996 [inline]
vzalloc+0x67/0x80 mm/vmalloc.c:3066
There are a number of ways it could be fixed. The page owner code could
be audited to strip GFP flags that allow sleeping but it'll impair the
functionality of PAGE_OWNER if allocations fail. The bulk allocator
could add a special case to release/reacquire the lock for prep_new_page
and lookup PCP after the lock is reacquired at the cost of performance.
The patches requiring prep could be tracked using the least significant
bit and looping through the array although it is more complicated for
the list interface. The options are relatively complex and the second
one still incurs a performance penalty when PAGE_OWNER is active so this
patch takes the simple approach -- disable bulk allocation of PAGE_OWNER is
active. The caller will be forced to allocate one page at a time incurring
a performance penalty but PAGE_OWNER is already a performance penalty.
Fixes: dbbee9d5cd83 ("mm/page_alloc: convert per-cpu list protection to local_lock")
Reported-by: Desmond Cheong Zhi Xi <[email protected]>
Reported-by: "Zhang, Qiang" <[email protected]>
Reported-and-tested-by: [email protected]
Signed-off-by: Mel Gorman <[email protected]>
---
mm/page_alloc.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3b97e17806be..6ef86f338151 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5239,6 +5239,18 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
if (nr_pages - nr_populated == 1)
goto failed;
+#ifdef CONFIG_PAGE_OWNER
+ /*
+ * PAGE_OWNER may recurse into the allocator to allocate space to
+ * save the stack with pagesets.lock held. Releasing/reacquiring
+ * removes much of the performance benefit of bulk allocation so
+ * force the caller to allocate one page at a time as it'll have
+ * similar performance to added complexity to the bulk allocator.
+ */
+ if (static_branch_unlikely(&page_owner_inited))
+ goto failed;
+#endif
+
/* May set ALLOC_NOFRAGMENT, fragmentation will return 1 page. */
gfp &= gfp_allowed_mask;
alloc_gfp = gfp;
On Thu, Jul 08, 2021 at 09:14:34AM +0100, Mel Gorman wrote:
> Syzbot is reporting potential deadlocks due to pagesets.lock when
> PAGE_OWNER is enabled. One example from Desmond Cheong Zhi Xi is
> as follows
>
> __alloc_pages_bulk()
> local_lock_irqsave(&pagesets.lock, flags) <---- outer lock here
> prep_new_page():
> post_alloc_hook():
> set_page_owner():
> __set_page_owner():
> save_stack():
> stack_depot_save():
> alloc_pages():
> alloc_page_interleave():
> __alloc_pages():
> get_page_from_freelist():
> rm_queue():
> rm_queue_pcplist():
> local_lock_irqsave(&pagesets.lock, flags);
> *** DEADLOCK ***
>
> Zhang, Qiang also reported
>
> BUG: sleeping function called from invalid context at mm/page_alloc.c:5179
> in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 1, name: swapper/0
> .....
> __dump_stack lib/dump_stack.c:79 [inline]
> dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:96
> ___might_sleep.cold+0x1f1/0x237 kernel/sched/core.c:9153
> prepare_alloc_pages+0x3da/0x580 mm/page_alloc.c:5179
> __alloc_pages+0x12f/0x500 mm/page_alloc.c:5375
> alloc_page_interleave+0x1e/0x200 mm/mempolicy.c:2147
> alloc_pages+0x238/0x2a0 mm/mempolicy.c:2270
> stack_depot_save+0x39d/0x4e0 lib/stackdepot.c:303
> save_stack+0x15e/0x1e0 mm/page_owner.c:120
> __set_page_owner+0x50/0x290 mm/page_owner.c:181
> prep_new_page mm/page_alloc.c:2445 [inline]
> __alloc_pages_bulk+0x8b9/0x1870 mm/page_alloc.c:5313
> alloc_pages_bulk_array_node include/linux/gfp.h:557 [inline]
> vm_area_alloc_pages mm/vmalloc.c:2775 [inline]
> __vmalloc_area_node mm/vmalloc.c:2845 [inline]
> __vmalloc_node_range+0x39d/0x960 mm/vmalloc.c:2947
> __vmalloc_node mm/vmalloc.c:2996 [inline]
> vzalloc+0x67/0x80 mm/vmalloc.c:3066
>
> There are a number of ways it could be fixed. The page owner code could
> be audited to strip GFP flags that allow sleeping but it'll impair the
> functionality of PAGE_OWNER if allocations fail. The bulk allocator
> could add a special case to release/reacquire the lock for prep_new_page
> and lookup PCP after the lock is reacquired at the cost of performance.
> The patches requiring prep could be tracked using the least significant
> bit and looping through the array although it is more complicated for
> the list interface. The options are relatively complex and the second
> one still incurs a performance penalty when PAGE_OWNER is active so this
> patch takes the simple approach -- disable bulk allocation of PAGE_OWNER is
^^^^
Minor nit: s/of/if
> active. The caller will be forced to allocate one page at a time incurring
> a performance penalty but PAGE_OWNER is already a performance penalty.
>
> Fixes: dbbee9d5cd83 ("mm/page_alloc: convert per-cpu list protection to local_lock")
> Reported-by: Desmond Cheong Zhi Xi <[email protected]>
> Reported-by: "Zhang, Qiang" <[email protected]>
> Reported-and-tested-by: [email protected]
> Signed-off-by: Mel Gorman <[email protected]>
> ---
> mm/page_alloc.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3b97e17806be..6ef86f338151 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5239,6 +5239,18 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
> if (nr_pages - nr_populated == 1)
> goto failed;
>
> +#ifdef CONFIG_PAGE_OWNER
> + /*
> + * PAGE_OWNER may recurse into the allocator to allocate space to
> + * save the stack with pagesets.lock held. Releasing/reacquiring
> + * removes much of the performance benefit of bulk allocation so
> + * force the caller to allocate one page at a time as it'll have
> + * similar performance to added complexity to the bulk allocator.
> + */
> + if (static_branch_unlikely(&page_owner_inited))
> + goto failed;
> +#endif
> +
> /* May set ALLOC_NOFRAGMENT, fragmentation will return 1 page. */
> gfp &= gfp_allowed_mask;
> alloc_gfp = gfp;
>
Acked-by: Rafael Aquini <[email protected]>
On Thu, Jul 08, 2021 at 09:10:18AM -0400, Rafael Aquini wrote:
> > There are a number of ways it could be fixed. The page owner code could
> > be audited to strip GFP flags that allow sleeping but it'll impair the
> > functionality of PAGE_OWNER if allocations fail. The bulk allocator
> > could add a special case to release/reacquire the lock for prep_new_page
> > and lookup PCP after the lock is reacquired at the cost of performance.
> > The patches requiring prep could be tracked using the least significant
If we're nitpicking changelogs, then s/patches/pages/
> > bit and looping through the array although it is more complicated for
> > the list interface. The options are relatively complex and the second
> > one still incurs a performance penalty when PAGE_OWNER is active so this
> > patch takes the simple approach -- disable bulk allocation of PAGE_OWNER is
> ^^^^
> Minor nit: s/of/if
>
> > active. The caller will be forced to allocate one page at a time incurring
> > a performance penalty but PAGE_OWNER is already a performance penalty.
The thought occurs that all pages allocated this way will have the same
stack. Someone suitably motivated could:
- Refcount the stacks managed by page_owner
- Generate the stack in the caller of alloc_bulk
- Pass the stack in to a new __set_page_owner()
That's a lot of work; I'm not going to do it, and I don't think Mel
should either. But if someone's looking for something to do ...