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idr: make idr_find rcu-safe 

Make idr_find rcu-safe: it can now be called inside an rcu_read critical
section.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Reviewed-by: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Jim Houston <jim.houston@comcast.net>
Cc: Pierre Peiffer <peifferp@gmail.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nadia Derbey 2008-07-25 01:48:01 -07:00 committed by Linus Torvalds
parent 3219b3b745
commit f9c46d6ea5
2 changed files with 22 additions and 5 deletions
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16
include/linux/idr.h
View File

@ -79,6 +79,22 @@ 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.
*/

11
lib/idr.c
View File

@ -456,7 +456,8 @@ 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)
{
@ -464,7 +465,7 @@ 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;
@ -474,7 +475,7 @@ 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);
}
@ -507,7 +508,7 @@ 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;
@ -515,7 +516,7 @@ 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) {