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shmem: fix smaps BUG sleeping while atomic

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smaps_pte_hole_lookup() is calling shmem_partial_swap_usage() with page
table lock held: but shmem_partial_swap_usage() does cond_resched_rcu() if
need_resched(): "BUG: sleeping function called from invalid context".

Since shmem_partial_swap_usage() is designed to count across a range, but
smaps_pte_hole_lookup() only calls it for a single page slot, just break
out of the loop on the last or only page, before checking need_resched().

Link: https://lkml.kernel.org/r/6fe3b3ec-abdf-332f-5c23-6a3b3a3b11a9@google.com
Fixes: 2301003215 ("mm/smaps: simplify shmem handling of pte holes")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>	[5.16+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2023-08-22 22:14:47 -07:00 committed by Andrew Morton
parent f84f62e699
commit e5548f85b4
1 changed files with 4 additions and 2 deletions
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6
mm/shmem.c
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@ -806,14 +806,16 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
XA_STATE(xas, &mapping->i_pages, start); XA_STATE(xas, &mapping->i_pages, start);
struct page *page; struct page *page;
unsigned long swapped = 0; unsigned long swapped = 0;
unsigned long max = end - 1;
rcu_read_lock(); rcu_read_lock();
xas_for_each(&xas, page, end - 1) { xas_for_each(&xas, page, max) {
if (xas_retry(&xas, page)) if (xas_retry(&xas, page))
continue; continue;
if (xa_is_value(page)) if (xa_is_value(page))
swapped++; swapped++;
if (xas.xa_index == max)
break;
if (need_resched()) { if (need_resched()) {
xas_pause(&xas); xas_pause(&xas);
cond_resched_rcu(); cond_resched_rcu();