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author | Michal Hocko <mhocko@suse.com> | 2020-06-04 01:03:25 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-06-04 05:09:49 +0200 |
commit | 2d3a36a47964371101d9a71691c18d59ee611e87 (patch) | |
tree | 7095a011438bf9ee1fac60a18ce6bb336b19d2f3 /mm/gup.c | |
parent | tools/vm/page_owner_sort.c: filter out unneeded line (diff) | |
download | linux-2d3a36a47964371101d9a71691c18d59ee611e87.tar.xz linux-2d3a36a47964371101d9a71691c18d59ee611e87.zip |
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>
Diffstat (limited to 'mm/gup.c')
-rw-r--r-- | mm/gup.c | 5 |
1 files changed, 5 insertions, 0 deletions
@@ -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, |