path: root/mm
diff options
authorMichal Hocko <mhocko@suse.com>2017-11-15 17:38:59 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-11-15 18:21:07 -0800
commit0a7f682d04652fd91de0cbc1ea3d7aa1e45611c7 (patch)
tree8b66408158a876f9854166795e124fb407d10ce4 /mm
parentfcdaf842bd8f538a88059ce0243bc2822ed1b0e0 (diff)
mm: do not rely on preempt_count in print_vma_addr
The preempt count check on print_vma_addr has been added by commit 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 commit 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@dhcp22.suse.cz Fixes: d99e1bd175f4 ("x86/entry/traps: Refactor preemption and interrupt flag handling") Signed-off-by: Michal Hocko <mhocko@suse.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Yang Shi <yang.s@alibaba-inc.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 3 insertions, 5 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 6dec21b182b0..85e7a87da79f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4485,17 +4485,15 @@ void print_vma_addr(char *prefix, unsigned long ip)
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))
- 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;