The patch titled
Subject: xarray: extract xa_zero_to_null
has been added to the -mm mm-nonmm-unstable branch. Its filename is
xarray-extract-xa_zero_to_null.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/xarray-extract-xa_zero_to_null.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: Tamir Duberstein <tamird@xxxxxxxxx>
Subject: xarray: extract xa_zero_to_null
Date: Tue, 12 Nov 2024 14:25:36 -0500
Patch series "xarray: extract __xa_cmpxchg_raw".
This series reduces duplication between __xa_cmpxchg and __xa_insert by
extracting a new function that does not coerce zero entries to null on the
return path.
The new function may be used by the upcoming Rust xarray abstraction in
its reservation API where it is useful to tell the difference between zero
entries and null slots.
This patch (of 2):
Reduce code duplication by extracting a static inline function that
returns its argument if it is non-zero and NULL otherwise.
This changes xas_result to check for errors before checking for zero but
this cannot change the behavior of existing callers:
- __xa_erase: passes the result of xas_store(_, NULL) which cannot fail.
- __xa_store: passes the result of xas_store(_, entry) which may fail.
xas_store calls xas_create when entry is not NULL which returns NULL
on error, which is immediately checked. This should not change
observable behavior.
- __xa_cmpxchg: passes the result of xas_load(_) which might be zero.
This would previously return NULL regardless of the outcome of
xas_store but xas_store cannot fail if xas_load returns zero
because there is no need to allocate memory.
- xa_store_range: same as __xa_erase.
Link: https://lkml.kernel.org/r/20241112-xarray-insert-cmpxchg-v1-0-dc2bdd8c4136@xxxxxxxxx
Link: https://lkml.kernel.org/r/20241112-xarray-insert-cmpxchg-v1-1-dc2bdd8c4136@xxxxxxxxx
Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxx>
Cc: Alice Ryhl <aliceryhl@xxxxxxxxxx>
Cc: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/xarray.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
--- a/lib/xarray.c~xarray-extract-xa_zero_to_null
+++ a/lib/xarray.c
@@ -435,6 +435,11 @@ static unsigned long max_index(void *ent
return (XA_CHUNK_SIZE << xa_to_node(entry)->shift) - 1;
}
+static inline void *xa_zero_to_null(void *entry)
+{
+ return xa_is_zero(entry) ? NULL : entry;
+}
+
static void xas_shrink(struct xa_state *xas)
{
struct xarray *xa = xas->xa;
@@ -451,8 +456,8 @@ static void xas_shrink(struct xa_state *
break;
if (!xa_is_node(entry) && node->shift)
break;
- if (xa_is_zero(entry) && xa_zero_busy(xa))
- entry = NULL;
+ if (xa_zero_busy(xa))
+ entry = xa_zero_to_null(entry);
xas->xa_node = XAS_BOUNDS;
RCU_INIT_POINTER(xa->xa_head, entry);
@@ -1474,9 +1479,7 @@ void *xa_load(struct xarray *xa, unsigne
rcu_read_lock();
do {
- entry = xas_load(&xas);
- if (xa_is_zero(entry))
- entry = NULL;
+ entry = xa_zero_to_null(xas_load(&xas));
} while (xas_retry(&xas, entry));
rcu_read_unlock();
@@ -1486,11 +1489,9 @@ EXPORT_SYMBOL(xa_load);
static void *xas_result(struct xa_state *xas, void *curr)
{
- if (xa_is_zero(curr))
- return NULL;
if (xas_error(xas))
curr = xas->xa_node;
- return curr;
+ return xa_zero_to_null(curr);
}
/**
_
Patches currently in -mm which might be from tamird@xxxxxxxxx are
xarray-extract-xa_zero_to_null.patch
xarray-extract-helper-from-__xa_insertcmpxchg.patch
