linux-kernel - [PATCH] lib/ida: Document locking requirements a bit better

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Message-Id: <20161026142739.20266-1-daniel.vetter@ffwll.ch>
Date:   Wed, 26 Oct 2016 16:27:39 +0200
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>, Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: [PATCH] lib/ida: Document locking requirements a bit better

I wanted to wrap a bunch of ida_simple_get calls into their own
locking, until I dug around and read the original commit message.
Stuff like this should imo be added to the kernel doc, let's do that.

Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Tejun Heo <tj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
---
 lib/idr.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lib/idr.c b/lib/idr.c
index 6098336df267..5508d7f6d7be 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -927,6 +927,9 @@ EXPORT_SYMBOL(ida_pre_get);
  * and go back to the ida_pre_get() call.  If the ida is full, it will
  * return %-ENOSPC.
  *
+ * Note that callers must ensure that concurrent access to @ida is not possible.
+ * When simplicity trumps concurrency needs look at ida_simple_get() instead.
+ *
  * @p_id returns a value in the range @starting_id ... %0x7fffffff.
  */
 int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)
@@ -1073,6 +1076,10 @@ EXPORT_SYMBOL(ida_destroy);
  * Allocates an id in the range start <= id < end, or returns -ENOSPC.
  * On memory allocation failure, returns -ENOMEM.
  *
+ * Compared to ida_get_new_above() this function does its own locking and hence
+ * is recommended everywhere where simplicity is preferred over the last bit of
+ * speed.
+ *
  * Use ida_simple_remove() to get rid of an id.
  */
 int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
@@ -1119,6 +1126,13 @@ EXPORT_SYMBOL(ida_simple_get);
  * ida_simple_remove - remove an allocated id.
  * @ida: the (initialized) ida.
  * @id: the id returned by ida_simple_get.
+ *
+ * Use to release an id allocated with ida_simple_get().
+ *
+ * Compared to ida_get_new_above() this function does its own locking and hence
+ * is recommended everywhere where simplicity is preferred over the last bit of
+ * speed.
+ *
  */
 void ida_simple_remove(struct ida *ida, unsigned int id)
 {
-- 
2.10.1