The patch titled
Subject: mm: do not rely on preempt_count in print_vma_addr
has been added to the -mm tree. Its filename is
mm-do-not-rely-on-preempt_count-in-print_vma_addr-was-re-mm-use-in_atomic-in-print_vma_addr.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-do-not-rely-on-preempt_count-in-print_vma_addr-was-re-mm-use-in_atomic-in-print_vma_addr.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-do-not-rely-on-preempt_count-in-print_vma_addr-was-re-mm-use-in_atomic-in-print_vma_addr.patch
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------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxxx>
Subject: mm: do not rely on preempt_count in print_vma_addr
The preempt count check on print_vma_addr has been added by e8bff74afbdb
("x86: fix "BUG: sleeping function called from invalid context" in
print_vma_addr()") and it relied on the elevated preempt count from
preempt_conditional_sti because preempt_count check doesn't work on non
preemptive kernels by default. The code has evolved though and
d99e1bd175f4 ("x86/entry/traps: Refactor preemption and interrupt flag
handling") has replaced preempt_conditional_sti by an explicit
preempt_disable which is noop on !PREEMPT so the check in print_vma_addr
is broken.
Fix the issue by using trylock on mmap_sem rather than chacking the
preempt count. The allocation we are relying on has to be GFP_NOWAIT as
well. There is a chance that we won't dump the vma state if the lock is
contended or the memory short but this is acceptable outcome and much less
fragile than the not working preemption check or tricks around it.
Link: http://lkml.kernel.org/r/20171106134031.g6dbelg55mrbyc6i@xxxxxxxxxxxxxx
Fixes: d99e1bd175f4 ("x86/entry/traps: Refactor preemption and interrupt flag handling")
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Yang Shi <yang.s@xxxxxxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff -puN mm/memory.c~mm-do-not-rely-on-preempt_count-in-print_vma_addr-was-re-mm-use-in_atomic-in-print_vma_addr mm/memory.c
--- a/mm/memory.c~mm-do-not-rely-on-preempt_count-in-print_vma_addr-was-re-mm-use-in_atomic-in-print_vma_addr
+++ a/mm/memory.c
@@ -4485,17 +4485,15 @@ void print_vma_addr(char *prefix, unsign
struct vm_area_struct *vma;
/*
- * Do not print if we are in atomic
- * contexts (in exception stacks, etc.):
+ * we might be running from an atomic context so we cannot sleep
*/
- if (preempt_count())
+ if (!down_read_trylock(&mm->mmap_sem))
return;
- down_read(&mm->mmap_sem);
vma = find_vma(mm, ip);
if (vma && vma->vm_file) {
struct file *f = vma->vm_file;
- char *buf = (char *)__get_free_page(GFP_KERNEL);
+ char *buf = (char *)__get_free_page(GFP_NOWAIT);
if (buf) {
char *p;
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
mm-memory_hotplug-do-not-back-off-draining-pcp-free-pages-from-kworker-context.patch
mm-drop-migrate-type-checks-from-has_unmovable_pages.patch
mm-distinguish-cma-and-movable-isolation-in-has_unmovable_pages.patch
mm-page_alloc-fail-has_unmovable_pages-when-seeing-reserved-pages.patch
mm-memory_hotplug-do-not-fail-offlining-too-early.patch
mm-memory_hotplug-remove-timeout-from-__offline_memory.patch
mm-hugetlb-drop-hugepages_treat_as_movable-sysctl.patch
mm-arch-remove-empty_bad_page.patch
mm-sparse-do-not-swamp-log-with-huge-vmemmap-allocation-failures.patch
mm-do-not-rely-on-preempt_count-in-print_vma_addr-was-re-mm-use-in_atomic-in-print_vma_addr.patch
fs-elf-drop-map_fixed-usage-from-elf_map.patch
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