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authorMichal Hocko2020-06-03 16:03:25 -0700
committerLinus Torvalds2020-06-03 20:09:49 -0700
commit2d3a36a47964371101d9a71691c18d59ee611e87 (patch)
tree7095a011438bf9ee1fac60a18ce6bb336b19d2f3
parent5b94ce2fcae2542c4d5d49176fa23eea638dc7b6 (diff)
mm, mempolicy: fix up gup usage in lookup_node
ba841078cd05 ("mm/mempolicy: Allow lookup_node() to handle fatal signal") has added a special casing for 0 return value because that was a possible gup return value when interrupted by fatal signal. This has been fixed by ae46d2aa6a7f ("mm/gup: Let __get_user_pages_locked() return -EINTR for fatal signal") in the mean time so ba841078cd05 can be reverted. This patch however doesn't go all the way to revert it because the check for 0 is wrong and confusing here. Firstly it is inherently unsafe to access the page when get_user_pages_locked returns 0 (aka no page returned). Fortunatelly this will not happen because get_user_pages_locked will not return 0 when nr_pages > 0 unless FOLL_NOWAIT is specified which is not the case here. Document this potential error code in gup code while we are at it. Signed-off-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Peter Xu <peterx@redhat.com> Link: http://lkml.kernel.org/r/20200421071026.18394-1-mhocko@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/gup.c5
-rw-r--r--mm/mempolicy.c5
2 files changed, 6 insertions, 4 deletions
diff --git a/mm/gup.c b/mm/gup.c
index 61ee405ec558..e19ff770eb4c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -989,6 +989,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
* -- If nr_pages is >0, but no pages were pinned, returns -errno.
* -- If nr_pages is >0, and some pages were pinned, returns the number of
* pages pinned. Again, this may be less than nr_pages.
+ * -- 0 return value is possible when the fault would need to be retried.
*
* The caller is responsible for releasing returned @pages, via put_page().
*
@@ -1265,6 +1266,10 @@ retry:
}
EXPORT_SYMBOL_GPL(fixup_user_fault);
+/*
+ * Please note that this function, unlike __get_user_pages will not
+ * return 0 for nr_pages > 0 without FOLL_NOWAIT
+ */
static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
struct mm_struct *mm,
unsigned long start,
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 48ba9729062e..1965e2681877 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -927,10 +927,7 @@ static int lookup_node(struct mm_struct *mm, unsigned long addr)
int locked = 1;
err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked);
- if (err == 0) {
- /* E.g. GUP interrupted by fatal signal */
- err = -EFAULT;
- } else if (err > 0) {
+ if (err > 0) {
err = page_to_nid(p);
put_page(p);
}