* [bug report] mm, compaction: capture a page under direct compaction
@ 2020-02-24 6:35 Dan Carpenter
2020-02-26 17:04 ` Vlastimil Babka
0 siblings, 1 reply; 5+ messages in thread
From: Dan Carpenter @ 2020-02-24 6:35 UTC (permalink / raw)
To: mgorman; +Cc: linux-mm
Hello Mel Gorman,
This is a semi-automatic email about new static checker warnings.
The patch 5e1f0f098b46: "mm, compaction: capture a page under direct
compaction" from Mar 5, 2019, leads to the following Smatch complaint:
mm/compaction.c:2321 compact_zone_order()
error: we previously assumed 'capture' could be null (see line 2313)
mm/compaction.c
2288 static enum compact_result compact_zone_order(struct zone *zone, int order,
2289 gfp_t gfp_mask, enum compact_priority prio,
2290 unsigned int alloc_flags, int classzone_idx,
2291 struct page **capture)
^^^^^^^
2292 {
2293 enum compact_result ret;
2294 struct compact_control cc = {
2295 .order = order,
2296 .search_order = order,
2297 .gfp_mask = gfp_mask,
2298 .zone = zone,
2299 .mode = (prio == COMPACT_PRIO_ASYNC) ?
2300 MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
2301 .alloc_flags = alloc_flags,
2302 .classzone_idx = classzone_idx,
2303 .direct_compaction = true,
2304 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
2305 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
2306 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
2307 };
2308 struct capture_control capc = {
2309 .cc = &cc,
2310 .page = NULL,
2311 };
2312
2313 if (capture)
^^^^^^^
Check for NULL
2314 current->capture_control = &capc;
2315
2316 ret = compact_zone(&cc, &capc);
2317
2318 VM_BUG_ON(!list_empty(&cc.freepages));
2319 VM_BUG_ON(!list_empty(&cc.migratepages));
2320
2321 *capture = capc.page;
^^^^^^^^
Unchecked dereference.
2322 current->capture_control = NULL;
2323
regards,
dan carpenter
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [bug report] mm, compaction: capture a page under direct compaction
2020-02-24 6:35 [bug report] mm, compaction: capture a page under direct compaction Dan Carpenter
@ 2020-02-26 17:04 ` Vlastimil Babka
2020-02-27 1:56 ` Andrew Morton
0 siblings, 1 reply; 5+ messages in thread
From: Vlastimil Babka @ 2020-02-26 17:04 UTC (permalink / raw)
To: Dan Carpenter, Andrew Morton; +Cc: mgorman, linux-mm
On 2/24/20 7:35 AM, Dan Carpenter wrote:
> Hello Mel Gorman,
>
> This is a semi-automatic email about new static checker warnings.
>
> The patch 5e1f0f098b46: "mm, compaction: capture a page under direct
> compaction" from Mar 5, 2019, leads to the following Smatch complaint:
>
> mm/compaction.c:2321 compact_zone_order()
> error: we previously assumed 'capture' could be null (see line 2313)
>
----8<----
From fb264bb52576a0582e8a92952cf91e8b61d105c3 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Wed, 26 Feb 2020 17:53:54 +0100
Subject: [PATCH] mm, compaction: fully assume capture can be NULL in
compact_zone_order()
Dan reports:
The patch 5e1f0f098b46: "mm, compaction: capture a page under direct
compaction" from Mar 5, 2019, leads to the following Smatch complaint:
mm/compaction.c:2321 compact_zone_order()
error: we previously assumed 'capture' could be null (see line 2313)
mm/compaction.c
2288 static enum compact_result compact_zone_order(struct zone *zone, int order,
2289 gfp_t gfp_mask, enum compact_priority prio,
2290 unsigned int alloc_flags, int classzone_idx,
2291 struct page **capture)
^^^^^^^
2313 if (capture)
^^^^^^^
Check for NULL
2314 current->capture_control = &capc;
2315
2316 ret = compact_zone(&cc, &capc);
2317
2318 VM_BUG_ON(!list_empty(&cc.freepages));
2319 VM_BUG_ON(!list_empty(&cc.migratepages));
2320
2321 *capture = capc.page;
^^^^^^^^
Unchecked dereference.
2322 current->capture_control = NULL;
2323
In practice this is not an issue, as the only caller path passes non-NULL
capture:
__alloc_pages_direct_compact()
struct page *page = NULL;
try_to_compact_pages(capture = &page);
compact_zone_order(capture = capture);
Hence no stable tag needed, but let's make this more robust and remove the
warning by assuming capture might be NULL in the second dereference.
Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
---
mm/compaction.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git mm/compaction.c mm/compaction.c
index 672d3c78c6ab..f4bb8091cf4f 100644
--- mm/compaction.c
+++ mm/compaction.c
@@ -2318,8 +2318,10 @@ static enum compact_result compact_zone_order(struct zone *zone, int order,
VM_BUG_ON(!list_empty(&cc.freepages));
VM_BUG_ON(!list_empty(&cc.migratepages));
- *capture = capc.page;
- current->capture_control = NULL;
+ if (capture) {
+ *capture = capc.page;
+ current->capture_control = NULL;
+ }
return ret;
}
--
2.25.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [bug report] mm, compaction: capture a page under direct compaction
2020-02-26 17:04 ` Vlastimil Babka
@ 2020-02-27 1:56 ` Andrew Morton
2020-02-27 7:45 ` Vlastimil Babka
0 siblings, 1 reply; 5+ messages in thread
From: Andrew Morton @ 2020-02-27 1:56 UTC (permalink / raw)
To: Vlastimil Babka; +Cc: Dan Carpenter, mgorman, linux-mm
On Wed, 26 Feb 2020 18:04:56 +0100 Vlastimil Babka <vbabka@suse.cz> wrote:
> On 2/24/20 7:35 AM, Dan Carpenter wrote:
> > Hello Mel Gorman,
> >
> > This is a semi-automatic email about new static checker warnings.
> >
> > The patch 5e1f0f098b46: "mm, compaction: capture a page under direct
> > compaction" from Mar 5, 2019, leads to the following Smatch complaint:
> >
> > mm/compaction.c:2321 compact_zone_order()
> > error: we previously assumed 'capture' could be null (see line 2313)
> >
>
> ----8<----
> >From fb264bb52576a0582e8a92952cf91e8b61d105c3 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Wed, 26 Feb 2020 17:53:54 +0100
> Subject: [PATCH] mm, compaction: fully assume capture can be NULL in
> compact_zone_order()
>
> Dan reports:
>
> The patch 5e1f0f098b46: "mm, compaction: capture a page under direct
> compaction" from Mar 5, 2019, leads to the following Smatch complaint:
>
> mm/compaction.c:2321 compact_zone_order()
> error: we previously assumed 'capture' could be null (see line 2313)
>
> mm/compaction.c
> 2288 static enum compact_result compact_zone_order(struct zone *zone, int order,
> 2289 gfp_t gfp_mask, enum compact_priority prio,
> 2290 unsigned int alloc_flags, int classzone_idx,
> 2291 struct page **capture)
> ^^^^^^^
>
> 2313 if (capture)
> ^^^^^^^
> Check for NULL
>
> 2314 current->capture_control = &capc;
> 2315
> 2316 ret = compact_zone(&cc, &capc);
> 2317
> 2318 VM_BUG_ON(!list_empty(&cc.freepages));
> 2319 VM_BUG_ON(!list_empty(&cc.migratepages));
> 2320
> 2321 *capture = capc.page;
> ^^^^^^^^
> Unchecked dereference.
>
> 2322 current->capture_control = NULL;
> 2323
>
> In practice this is not an issue, as the only caller path passes non-NULL
> capture:
>
> __alloc_pages_direct_compact()
> struct page *page = NULL;
> try_to_compact_pages(capture = &page);
> compact_zone_order(capture = capture);
>
> Hence no stable tag needed, but let's make this more robust and remove the
> warning by assuming capture might be NULL in the second dereference.
>
> ...
>
> --- mm/compaction.c
> +++ mm/compaction.c
> @@ -2318,8 +2318,10 @@ static enum compact_result compact_zone_order(struct zone *zone, int order,
> VM_BUG_ON(!list_empty(&cc.freepages));
> VM_BUG_ON(!list_empty(&cc.migratepages));
>
> - *capture = capc.page;
> - current->capture_control = NULL;
> + if (capture) {
> + *capture = capc.page;
> + current->capture_control = NULL;
> + }
>
> return ret;
> }
Why don't we instead remove the first check for NULL? Remove some dead
code instead of adding some?
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [bug report] mm, compaction: capture a page under direct compaction
2020-02-27 1:56 ` Andrew Morton
@ 2020-02-27 7:45 ` Vlastimil Babka
2020-02-28 13:47 ` Mel Gorman
0 siblings, 1 reply; 5+ messages in thread
From: Vlastimil Babka @ 2020-02-27 7:45 UTC (permalink / raw)
To: Andrew Morton; +Cc: Dan Carpenter, mgorman, linux-mm
On 2/27/20 2:56 AM, Andrew Morton wrote:
> On Wed, 26 Feb 2020 18:04:56 +0100 Vlastimil Babka <vbabka@suse.cz> wrote:
>
>> On 2/24/20 7:35 AM, Dan Carpenter wrote:
>> > Hello Mel Gorman,
>> >
>> > This is a semi-automatic email about new static checker warnings.
>> >
>> > The patch 5e1f0f098b46: "mm, compaction: capture a page under direct
>> > compaction" from Mar 5, 2019, leads to the following Smatch complaint:
>> >
>> > mm/compaction.c:2321 compact_zone_order()
>> > error: we previously assumed 'capture' could be null (see line 2313)
>> >
>>
>> ----8<----
>> >From fb264bb52576a0582e8a92952cf91e8b61d105c3 Mon Sep 17 00:00:00 2001
>> From: Vlastimil Babka <vbabka@suse.cz>
>> Date: Wed, 26 Feb 2020 17:53:54 +0100
>> Subject: [PATCH] mm, compaction: fully assume capture can be NULL in
>> compact_zone_order()
>>
>
> Why don't we instead remove the first check for NULL? Remove some dead
> code instead of adding some?
>
Sure, works too. Anyone creating a new caller and trying to pass NULL will
crash quickly.
----8<----
From 3118d9bea8a0fcef294915220f824674fb039ec3 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Wed, 26 Feb 2020 17:53:54 +0100
Subject: [PATCH] mm, compaction: fully assume capture is not NULL in
compact_zone_order()
Dan reports:
The patch 5e1f0f098b46: "mm, compaction: capture a page under direct
compaction" from Mar 5, 2019, leads to the following Smatch complaint:
mm/compaction.c:2321 compact_zone_order()
error: we previously assumed 'capture' could be null (see line 2313)
mm/compaction.c
2288 static enum compact_result compact_zone_order(struct zone *zone, int order,
2289 gfp_t gfp_mask, enum compact_priority prio,
2290 unsigned int alloc_flags, int classzone_idx,
2291 struct page **capture)
^^^^^^^
2313 if (capture)
^^^^^^^
Check for NULL
2314 current->capture_control = &capc;
2315
2316 ret = compact_zone(&cc, &capc);
2317
2318 VM_BUG_ON(!list_empty(&cc.freepages));
2319 VM_BUG_ON(!list_empty(&cc.migratepages));
2320
2321 *capture = capc.page;
^^^^^^^^
Unchecked dereference.
2322 current->capture_control = NULL;
2323
In practice this is not an issue, as the only caller path passes non-NULL
capture:
__alloc_pages_direct_compact()
struct page *page = NULL;
try_to_compact_pages(capture = &page);
compact_zone_order(capture = capture);
So let's remove the unnecessary check, which should also make Smatch happy.
Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
---
mm/compaction.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git mm/compaction.c mm/compaction.c
index 672d3c78c6ab..35c991fbf983 100644
--- mm/compaction.c
+++ mm/compaction.c
@@ -2310,8 +2310,7 @@ static enum compact_result compact_zone_order(struct zone *zone, int order,
.page = NULL,
};
- if (capture)
- current->capture_control = &capc;
+ current->capture_control = &capc;
ret = compact_zone(&cc, &capc);
@@ -2333,6 +2332,7 @@ int sysctl_extfrag_threshold = 500;
* @alloc_flags: The allocation flags of the current allocation
* @ac: The context of current allocation
* @prio: Determines how hard direct compaction should try to succeed
+ * @capture: Pointer to free page created by compaction will be stored here
*
* This is the main entry point for direct page compaction.
*/
--
2.25.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [bug report] mm, compaction: capture a page under direct compaction
2020-02-27 7:45 ` Vlastimil Babka
@ 2020-02-28 13:47 ` Mel Gorman
0 siblings, 0 replies; 5+ messages in thread
From: Mel Gorman @ 2020-02-28 13:47 UTC (permalink / raw)
To: Vlastimil Babka; +Cc: Andrew Morton, Dan Carpenter, linux-mm
On Thu, Feb 27, 2020 at 08:45:46AM +0100, Vlastimil Babka wrote:
Bit late to the game but;
> ----8<----
> From 3118d9bea8a0fcef294915220f824674fb039ec3 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Wed, 26 Feb 2020 17:53:54 +0100
> Subject: [PATCH] mm, compaction: fully assume capture is not NULL in
> compact_zone_order()
>
> Dan reports:
>
> The patch 5e1f0f098b46: "mm, compaction: capture a page under direct
> compaction" from Mar 5, 2019, leads to the following Smatch complaint:
>
> mm/compaction.c:2321 compact_zone_order()
> error: we previously assumed 'capture' could be null (see line 2313)
>
> mm/compaction.c
> 2288 static enum compact_result compact_zone_order(struct zone *zone, int order,
> 2289 gfp_t gfp_mask, enum compact_priority prio,
> 2290 unsigned int alloc_flags, int classzone_idx,
> 2291 struct page **capture)
> ^^^^^^^
>
> 2313 if (capture)
> ^^^^^^^
> Check for NULL
>
> 2314 current->capture_control = &capc;
> 2315
> 2316 ret = compact_zone(&cc, &capc);
> 2317
> 2318 VM_BUG_ON(!list_empty(&cc.freepages));
> 2319 VM_BUG_ON(!list_empty(&cc.migratepages));
> 2320
> 2321 *capture = capc.page;
> ^^^^^^^^
> Unchecked dereference.
>
> 2322 current->capture_control = NULL;
> 2323
>
> In practice this is not an issue, as the only caller path passes non-NULL
> capture:
>
> __alloc_pages_direct_compact()
> struct page *page = NULL;
> try_to_compact_pages(capture = &page);
> compact_zone_order(capture = capture);
>
> So let's remove the unnecessary check, which should also make Smatch happy.
>
> Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction")
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Suggested-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
--
Mel Gorman
SUSE Labs
^ permalink raw reply [flat|nested] 5+ messages in thread
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2020-02-24 6:35 [bug report] mm, compaction: capture a page under direct compaction Dan Carpenter
2020-02-26 17:04 ` Vlastimil Babka
2020-02-27 1:56 ` Andrew Morton
2020-02-27 7:45 ` Vlastimil Babka
2020-02-28 13:47 ` Mel Gorman
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