Commit 3e6628c4 authored Apr 29, 2013 by Jeff Layton Committed by Linus Torvalds Apr 29, 2013

idr: introduce idr_alloc_cyclic()



As Tejun points out, there are several users of the IDR facility that
attempt to use it in a cyclic fashion.  These users are likely to see
-ENOSPC errors after the counter wraps one or more times however.

This patchset adds a new idr_alloc_cyclic routine and converts several
of these users to it.  Many of these users are in obscure parts of the
kernel, and I don't have a good way to test some of them.  The change is
pretty straightforward though, so hopefully it won't be an issue.

There is one other cyclic user of idr_alloc that I didn't touch in
ipc/util.c.  That one is doing some strange stuff that I didn't quite
understand, but it looks like it should probably be converted later
somehow.

This patch:

Thus spake Tejun Heo:

    Ooh, BTW, the cyclic allocation is broken.  It's prone to -ENOSPC
    after the first wraparound.  There are several cyclic users in the
    kernel and I think it probably would be best to implement cyclic
    support in idr.

This patch does that by adding new idr_alloc_cyclic function that such
users in the kernel can use.  With this, there's no need for a caller to
keep track of the last value used as that's now tracked internally.  This
should prevent the ENOSPC problems that can hit when the "last allocated"
counter exceeds INT_MAX.

Later patches will convert existing cyclic users to the new interface.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Eric Paris <eparis@parisplace.org>
Cc: Jack Morgenstein <jackm@dev.mellanox.co.il>
Cc: John McCutchan <john@johnmccutchan.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: Or Gerlitz <ogerlitz@mellanox.com>
Cc: Robert Love <rlove@rlove.org>
Cc: Roland Dreier <roland@purestorage.com>
Cc: Sridhar Samudrala <sri@us.ibm.com>
Cc: Steve Wise <swise@opengridcomputing.com>
Cc: Tom Tucker <tom@opengridcomputing.com>
Cc: Vlad Yasevich <vyasevich@gmail.com>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 27cf10e1

include/linux/idr.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -42,6 +42,7 @@ struct idr {
		struct idr_layer *id_free;
		int layers; /* only valid w/o concurrent changes */
		int id_free_cnt;
		int cur; /* current pos for cyclic allocation */
		spinlock_t lock;
		};

		@@ -75,6 +76,7 @@ struct idr {
		void idr_find_slowpath(struct idr idp, int id);
		void idr_preload(gfp_t gfp_mask);
		int idr_alloc(struct idr idp, void ptr, int start, int end, gfp_t gfp_mask);
		int idr_alloc_cyclic(struct idr idr, void ptr, int start, int end, gfp_t gfp_mask);
		int idr_for_each(struct idr *idp,
		int (fn)(int id, void p, void data), void data);
		void idr_get_next(struct idr idp, int *nextid);

lib/idr.c

+27 −0

Original line number	Diff line number	Diff line
		@@ -495,6 +495,33 @@ int idr_alloc(struct idr idr, void ptr, int start, int end, gfp_t gfp_mask)
		}
		EXPORT_SYMBOL_GPL(idr_alloc);

		/**
		* idr_alloc_cyclic - allocate new idr entry in a cyclical fashion
		* @idr: the (initialized) idr
		* @ptr: pointer to be associated with the new id
		* @start: the minimum id (inclusive)
		* @end: the maximum id (exclusive, <= 0 for max)
		* @gfp_mask: memory allocation flags
		*
		* Essentially the same as idr_alloc, but prefers to allocate progressively
		* higher ids if it can. If the "cur" counter wraps, then it will start again
		* at the "start" end of the range and allocate one that has already been used.
		*/
		int idr_alloc_cyclic(struct idr idr, void ptr, int start, int end,
		gfp_t gfp_mask)
		{
		int id;

		id = idr_alloc(idr, ptr, max(start, idr->cur), end, gfp_mask);
		if (id == -ENOSPC)
		id = idr_alloc(idr, ptr, start, end, gfp_mask);

		if (likely(id >= 0))
		idr->cur = id + 1;
		return id;
		}
		EXPORT_SYMBOL(idr_alloc_cyclic);

		static void idr_remove_warning(int id)
		{
		printk(KERN_WARNING