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Subject[PATCH 4.9 034/102] mm/vmscan.c: fix unsequenced modification and access warning
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nick Desaulniers <nick.desaulniers@gmail.com>

commit f2f43e566a02a3bdde0a65e6a2e88d707c212a29 upstream.

Clang and its -Wunsequenced emits a warning

mm/vmscan.c:2961:25: error: unsequenced modification and access to 'gfp_mask' [-Wunsequenced]
.gfp_mask = (gfp_mask = current_gfp_context(gfp_mask)),
^

While it is not clear to me whether the initialization code violates the
specification (6.7.8 par 19 (ISO/IEC 9899) looks like it disagrees) the
code is quite confusing and worth cleaning up anyway. Fix this by
reusing sc.gfp_mask rather than the updated input gfp_mask parameter.

Link: http://lkml.kernel.org/r/20170510154030.10720-1-nick.desaulniers@gmail.com
Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[natechancellor: Adjust context due to abscence of 7dea19f9ee63]
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/vmscan.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2966,7 +2966,7 @@ unsigned long try_to_free_pages(struct z
unsigned long nr_reclaimed;
struct scan_control sc = {
.nr_to_reclaim = SWAP_CLUSTER_MAX,
- .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
+ .gfp_mask = memalloc_noio_flags(gfp_mask),
.reclaim_idx = gfp_zone(gfp_mask),
.order = order,
.nodemask = nodemask,
@@ -2981,12 +2981,12 @@ unsigned long try_to_free_pages(struct z
* 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);
@@ -3749,16 +3749,15 @@ static int __node_reclaim(struct pglist_
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 = memalloc_noio_flags(gfp_mask)),
+ .gfp_mask = memalloc_noio_flags(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();
@@ -3768,7 +3767,7 @@ static int __node_reclaim(struct pglist_
* 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;


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