The patch titled
Subject: Xarray: move forward index correctly in xas_pause()
has been added to the -mm mm-nonmm-unstable branch. Its filename is
xarray-move-forward-index-correctly-in-xas_pause.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/xarray-move-forward-index-correctly-in-xas_pause.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
Subject: Xarray: move forward index correctly in xas_pause()
Date: Fri, 13 Dec 2024 20:25:20 +0800
After xas_load(), xas->index could point to mid of found multi-index entry
and xas->index's bits under node->shift maybe non-zero. The afterward
xas_pause() will move forward xas->index with xa->node->shift with bits
under node->shift un-masked and thus skip some index unexpectedly.
Consider following case:
Assume XA_CHUNK_SHIFT is 4.
xa_store_range(xa, 16, 31, ...)
xa_store(xa, 32, ...)
XA_STATE(xas, xa, 17);
xas_for_each(&xas,...)
xas_load(&xas)
/* xas->index = 17, xas->xa_offset = 1, xas->xa_node->xa_shift = 4 */
xas_pause()
/* xas->index = 33, xas->xa_offset = 2, xas->xa_node->xa_shift = 4 */
As we can see, index of 32 is skipped unexpectedly.
Fix this by mask bit under node->xa_shift when move forward index in
xas_pause().
For now, this will not cause serious problems. Only minor problem like
cachestat return less number of page status could happen.
Link: https://lkml.kernel.org/r/20241213122523.12764-3-shikemeng@xxxxxxxxxxxxxxx
Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/test_xarray.c | 35 +++++++++++++++++++++++++++++++++++
lib/xarray.c | 1 +
2 files changed, 36 insertions(+)
--- a/lib/test_xarray.c~xarray-move-forward-index-correctly-in-xas_pause
+++ a/lib/test_xarray.c
@@ -1511,6 +1511,41 @@ static noinline void check_pause(struct
XA_BUG_ON(xa, count != order_limit);
xa_destroy(xa);
+
+ index = 0;
+ for (order = XA_CHUNK_SHIFT; order > 0; order--) {
+ XA_BUG_ON(xa, xa_store_order(xa, index, order,
+ xa_mk_index(index), GFP_KERNEL));
+ index += 1UL << order;
+ }
+
+ index = 0;
+ count = 0;
+ xas_set(&xas, 0);
+ rcu_read_lock();
+ xas_for_each(&xas, entry, ULONG_MAX) {
+ XA_BUG_ON(xa, entry != xa_mk_index(index));
+ index += 1UL << (XA_CHUNK_SHIFT - count);
+ count++;
+ }
+ rcu_read_unlock();
+ XA_BUG_ON(xa, count != XA_CHUNK_SHIFT);
+
+ index = 0;
+ count = 0;
+ xas_set(&xas, XA_CHUNK_SIZE / 2 + 1);
+ rcu_read_lock();
+ xas_for_each(&xas, entry, ULONG_MAX) {
+ XA_BUG_ON(xa, entry != xa_mk_index(index));
+ index += 1UL << (XA_CHUNK_SHIFT - count);
+ count++;
+ xas_pause(&xas);
+ }
+ rcu_read_unlock();
+ XA_BUG_ON(xa, count != XA_CHUNK_SHIFT);
+
+ xa_destroy(xa);
+
}
static noinline void check_move_tiny(struct kunit *test)
--- a/lib/xarray.c~xarray-move-forward-index-correctly-in-xas_pause
+++ a/lib/xarray.c
@@ -1152,6 +1152,7 @@ void xas_pause(struct xa_state *xas)
if (!xa_is_sibling(xa_entry(xas->xa, node, offset)))
break;
}
+ xas->xa_index &= ~0UL << node->shift;
xas->xa_index += (offset - xas->xa_offset) << node->shift;
if (xas->xa_index == 0)
xas->xa_node = XAS_BOUNDS;
_
Patches currently in -mm which might be from shikemeng@xxxxxxxxxxxxxxx are
xarray-do-not-return-sibling-entries-from-xas_find_marked.patch
xarray-move-forward-index-correctly-in-xas_pause.patch
xarray-distinguish-large-entries-correctly-in-xas_split_alloc.patch
xarray-remove-repeat-check-in-xas_squash_marks.patch
xarray-use-xa_mark_t-in-xas_squash_marks-to-keep-code-consistent.patch
