The patch titled
idr: make idr_find rcu-safe
has been added to the -mm tree. Its filename is
idr-make-idr_find-rcu-safe.patch
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------------------------------------------------------
Subject: idr: make idr_find rcu-safe
From: Nadia Derbey <Nadia.Derbey@xxxxxxxx>
Make idr_find rcu-safe: it can now be called inside an rcu_read critical
section.
Signed-off-by: Nadia Derbey <Nadia.Derbey@xxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Jim Houston <jim.houston@xxxxxxxxxxx>
Cc: Pierre Peiffer <peifferp@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/idr.h | 16 ++++++++++++++++
lib/idr.c | 11 ++++++-----
2 files changed, 22 insertions(+), 5 deletions(-)
diff -puN include/linux/idr.h~idr-make-idr_find-rcu-safe include/linux/idr.h
--- a/include/linux/idr.h~idr-make-idr_find-rcu-safe
+++ a/include/linux/idr.h
@@ -80,6 +80,22 @@ struct idr {
#define _idr_rc_to_errno(rc) ((rc) == -1 ? -EAGAIN : -ENOSPC)
+/**
+ * idr synchronization (stolen from radix-tree.h)
+ *
+ * idr_find() is able to be called locklessly, using RCU. The caller must
+ * ensure calls to this function are made within rcu_read_lock() regions.
+ * Other readers (lock-free or otherwise) and modifications may be running
+ * concurrently.
+ *
+ * It is still required that the caller manage the synchronization and
+ * lifetimes of the items. So if RCU lock-free lookups are used, typically
+ * this would mean that the items have their own locks, or are amenable to
+ * lock-free access; and that the items are freed by RCU (or only freed after
+ * having been deleted from the idr tree *and* a synchronize_rcu() grace
+ * period).
+ */
+
/*
* This is what we export.
*/
diff -puN lib/idr.c~idr-make-idr_find-rcu-safe lib/idr.c
--- a/lib/idr.c~idr-make-idr_find-rcu-safe
+++ a/lib/idr.c
@@ -459,7 +459,8 @@ EXPORT_SYMBOL(idr_destroy);
* return indicates that @id is not valid or you passed %NULL in
* idr_get_new().
*
- * The caller must serialize idr_find() vs idr_get_new() and idr_remove().
+ * This function can be called under rcu_read_lock(), given that the leaf
+ * pointers lifetimes are correctly managed.
*/
void *idr_find(struct idr *idp, int id)
{
@@ -467,7 +468,7 @@ void *idr_find(struct idr *idp, int id)
struct idr_layer *p;
n = idp->layers * IDR_BITS;
- p = idp->top;
+ p = rcu_dereference(idp->top);
/* Mask off upper bits we don't use for the search. */
id &= MAX_ID_MASK;
@@ -477,7 +478,7 @@ void *idr_find(struct idr *idp, int id)
while (n > 0 && p) {
n -= IDR_BITS;
- p = p->ary[(id >> n) & IDR_MASK];
+ p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
}
return((void *)p);
}
@@ -510,7 +511,7 @@ int idr_for_each(struct idr *idp,
struct idr_layer **paa = &pa[0];
n = idp->layers * IDR_BITS;
- p = idp->top;
+ p = rcu_dereference(idp->top);
max = 1 << n;
id = 0;
@@ -518,7 +519,7 @@ int idr_for_each(struct idr *idp,
while (n > 0 && p) {
n -= IDR_BITS;
*paa++ = p;
- p = p->ary[(id >> n) & IDR_MASK];
+ p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
}
if (p) {
_
Patches currently in -mm which might be from Nadia.Derbey@xxxxxxxx are
idr-change-the-idr-structure.patch
idr-rename-some-of-the-idr-apis-internal-routines.patch
idr-fix-a-printk-call.patch
idr-error-checking-factorization.patch
idr-make-idr_get_new-rcu-safe.patch
idr-make-idr_find-rcu-safe.patch
idr-make-idr_remove-rcu-safe.patch
ipc-call-idr_find-without-locking-in-ipc_lock.patch
ipc-get-rid-of-ipc_lock_down.patch
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