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Subject[Patch v2] mm/vmscan: fix unsequenced modification and access warning
Date
Clang flags this file with the -Wunsequenced error that GCC does not
have.

unsequenced modification and access to 'gfp_mask'

It seems that gfp_mask is both read and written without a sequence point
in between, which is undefined behavior.

Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
---
Changes in v2:
- don't assign back to gfp_mask, reuse sc.gfp_mask
- initialize reclaim_idx directly, without classzone_idx

mm/vmscan.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4e7ed65842af..d32c42d17935 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2958,7 +2958,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
unsigned long nr_reclaimed;
struct scan_control sc = {
.nr_to_reclaim = SWAP_CLUSTER_MAX,
- .gfp_mask = (gfp_mask = current_gfp_context(gfp_mask)),
+ .gfp_mask = current_gfp_context(gfp_mask),
.reclaim_idx = gfp_zone(gfp_mask),
.order = order,
.nodemask = nodemask,
@@ -2973,12 +2973,12 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
* 1 is returned so that the page allocator does not OOM kill at this
* point.
*/
- if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
+ if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
return 1;

trace_mm_vmscan_direct_reclaim_begin(order,
sc.may_writepage,
- gfp_mask,
+ sc.gfp_mask,
sc.reclaim_idx);

nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
@@ -3763,16 +3763,15 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
const unsigned long nr_pages = 1 << order;
struct task_struct *p = current;
struct reclaim_state reclaim_state;
- int classzone_idx = gfp_zone(gfp_mask);
struct scan_control sc = {
.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
- .gfp_mask = (gfp_mask = current_gfp_context(gfp_mask)),
+ .gfp_mask = current_gfp_context(gfp_mask),
.order = order,
.priority = NODE_RECLAIM_PRIORITY,
.may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
.may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
.may_swap = 1,
- .reclaim_idx = classzone_idx,
+ .reclaim_idx = gfp_zone(gfp_mask),
};

cond_resched();
@@ -3782,7 +3781,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
* and RECLAIM_UNMAP.
*/
p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
- lockdep_set_current_reclaim_state(gfp_mask);
+ lockdep_set_current_reclaim_state(sc.gfp_mask);
reclaim_state.reclaimed_slab = 0;
p->reclaim_state = &reclaim_state;

--
2.11.0
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