From 4af679cd7cbb0a0d8774b5cdb34bffcaa4e86e52 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 13 Dec 2011 10:36:20 +0100 Subject: kref: Inline all functions These are tiny functions, there's no point in having them out-of-line. Cc: Alexey Dobriyan Cc: Eric Dumazet Cc: Ingo Molnar Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-8eccvi2ur2fzgi00xdjlbf5z@git.kernel.org Signed-off-by: Greg Kroah-Hartman --- include/linux/kref.h | 80 ++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 75 insertions(+), 5 deletions(-) (limited to 'include/linux/kref.h') diff --git a/include/linux/kref.h b/include/linux/kref.h index d4a62ab2ee5e..1cbae9f2ef77 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -16,15 +16,85 @@ #define _KREF_H_ #include +#include struct kref { atomic_t refcount; }; -void kref_init(struct kref *kref); -void kref_get(struct kref *kref); -int kref_put(struct kref *kref, void (*release) (struct kref *kref)); -int kref_sub(struct kref *kref, unsigned int count, - void (*release) (struct kref *kref)); +/** + * kref_init - initialize object. + * @kref: object in question. + */ +static inline void kref_init(struct kref *kref) +{ + atomic_set(&kref->refcount, 1); + smp_mb(); +} + +/** + * kref_get - increment refcount for object. + * @kref: object. + */ +static inline void kref_get(struct kref *kref) +{ + WARN_ON(!atomic_read(&kref->refcount)); + atomic_inc(&kref->refcount); + smp_mb__after_atomic_inc(); +} + +/** + * kref_put - decrement refcount for object. + * @kref: object. + * @release: pointer to the function that will clean up the object when the + * last reference to the object is released. + * This pointer is required, and it is not acceptable to pass kfree + * in as this function. + * + * Decrement the refcount, and if 0, call release(). + * Return 1 if the object was removed, otherwise return 0. Beware, if this + * function returns 0, you still can not count on the kref from remaining in + * memory. Only use the return value if you want to see if the kref is now + * gone, not present. + */ +static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) +{ + WARN_ON(release == NULL); + WARN_ON(release == (void (*)(struct kref *))kfree); + + if (atomic_dec_and_test(&kref->refcount)) { + release(kref); + return 1; + } + return 0; +} + + +/** + * kref_sub - subtract a number of refcounts for object. + * @kref: object. + * @count: Number of recounts to subtract. + * @release: pointer to the function that will clean up the object when the + * last reference to the object is released. + * This pointer is required, and it is not acceptable to pass kfree + * in as this function. + * + * Subtract @count from the refcount, and if 0, call release(). + * Return 1 if the object was removed, otherwise return 0. Beware, if this + * function returns 0, you still can not count on the kref from remaining in + * memory. Only use the return value if you want to see if the kref is now + * gone, not present. + */ +static inline int kref_sub(struct kref *kref, unsigned int count, + void (*release)(struct kref *kref)) +{ + WARN_ON(release == NULL); + WARN_ON(release == (void (*)(struct kref *))kfree); + if (atomic_sub_and_test((int) count, &kref->refcount)) { + release(kref); + return 1; + } + return 0; +} #endif /* _KREF_H_ */ -- cgit From 47dbd7d90ad80edb67822f327241edcab8f3f46f Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Sat, 10 Dec 2011 11:43:43 +0100 Subject: kref: Implement kref_put in terms of kref_sub Less lines of code is better. Cc: Alexey Dobriyan Cc: Eric Dumazet Cc: Ingo Molnar Signed-off-by: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman --- include/linux/kref.h | 28 ++++++++++------------------ 1 file changed, 10 insertions(+), 18 deletions(-) (limited to 'include/linux/kref.h') diff --git a/include/linux/kref.h b/include/linux/kref.h index 1cbae9f2ef77..fa9907a541e2 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -44,57 +44,49 @@ static inline void kref_get(struct kref *kref) } /** - * kref_put - decrement refcount for object. + * kref_sub - subtract a number of refcounts for object. * @kref: object. + * @count: Number of recounts to subtract. * @release: pointer to the function that will clean up the object when the * last reference to the object is released. * This pointer is required, and it is not acceptable to pass kfree * in as this function. * - * Decrement the refcount, and if 0, call release(). + * Subtract @count from the refcount, and if 0, call release(). * Return 1 if the object was removed, otherwise return 0. Beware, if this * function returns 0, you still can not count on the kref from remaining in * memory. Only use the return value if you want to see if the kref is now * gone, not present. */ -static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) +static inline int kref_sub(struct kref *kref, unsigned int count, + void (*release)(struct kref *kref)) { WARN_ON(release == NULL); WARN_ON(release == (void (*)(struct kref *))kfree); - if (atomic_dec_and_test(&kref->refcount)) { + if (atomic_sub_and_test((int) count, &kref->refcount)) { release(kref); return 1; } return 0; } - /** - * kref_sub - subtract a number of refcounts for object. + * kref_put - decrement refcount for object. * @kref: object. - * @count: Number of recounts to subtract. * @release: pointer to the function that will clean up the object when the * last reference to the object is released. * This pointer is required, and it is not acceptable to pass kfree * in as this function. * - * Subtract @count from the refcount, and if 0, call release(). + * Decrement the refcount, and if 0, call release(). * Return 1 if the object was removed, otherwise return 0. Beware, if this * function returns 0, you still can not count on the kref from remaining in * memory. Only use the return value if you want to see if the kref is now * gone, not present. */ -static inline int kref_sub(struct kref *kref, unsigned int count, - void (*release)(struct kref *kref)) +static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) { - WARN_ON(release == NULL); - WARN_ON(release == (void (*)(struct kref *))kfree); - - if (atomic_sub_and_test((int) count, &kref->refcount)) { - release(kref); - return 1; - } - return 0; + return kref_sub(kref, 1, release); } #endif /* _KREF_H_ */ -- cgit From 3c8ed88974472b928489e3943616500ce2ad0cd8 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Sat, 10 Dec 2011 11:43:44 +0100 Subject: kref: Remove the memory barriers Commit 1b0b3b9980e ("kref: fix CPU ordering with respect to krefs") wrongly adds memory barriers to kref. It states: some atomic operations are only atomic, not ordered. Thus a CPU is allowed to reorder memory references to an object to before the reference is obtained. This fixes it. While true, it fails to show why this is a problem. I say it is not a problem because if there is a race with kref_put() such that we could end up referencing a free'd object without this memory barrier, we would still have that race with the memory barrier. The kref_put() in question could complete (and free the object) before the atomic_inc() and we'd still be up shit creek. The kref_init() case is even worse, if your object is published at this time you're so wrong the memory barrier won't make a difference what so ever. If its not published, the act of publishing should include the needed barriers/locks to make sure all writes prior to the act of publishing are complete such that others will only observe a complete object. Cc: Alexey Dobriyan Cc: Eric Dumazet Cc: Ingo Molnar Cc: Oliver Neukum Signed-off-by: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman --- include/linux/kref.h | 2 -- 1 file changed, 2 deletions(-) (limited to 'include/linux/kref.h') diff --git a/include/linux/kref.h b/include/linux/kref.h index fa9907a541e2..d66c88a3b48c 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -29,7 +29,6 @@ struct kref { static inline void kref_init(struct kref *kref) { atomic_set(&kref->refcount, 1); - smp_mb(); } /** @@ -40,7 +39,6 @@ static inline void kref_get(struct kref *kref) { WARN_ON(!atomic_read(&kref->refcount)); atomic_inc(&kref->refcount); - smp_mb__after_atomic_inc(); } /** -- cgit From 6261ddee70174372d6a75601f40719b7a5392f3f Mon Sep 17 00:00:00 2001 From: Greg Kroah-Hartman Date: Wed, 14 Dec 2011 11:19:07 -0800 Subject: kref: fix up the kfree build problems It turns out that some memory allocators use kobjects, which use krefs, and kref.h was wanting to figure out the address of kfree(), which ended up in a loop. kfree was only being needed for a warning to tell the caller that they were doing something stupid. Now we just move that warning into the comments for the functions, which results in a bit more fun as everyone enjoys digging for people to mock at times of boredom. So, remove the dependancy of slab.h on kref.h, and fix up the other include file as well (we really only need bug.h and atomic.h, not types.h). Reported-by: Stephen Rothwell Cc: Peter Zijlstra Cc: Alexey Dobriyan Cc: Eric Dumazet Cc: Ingo Molnar Cc: Oliver Neukum Signed-off-by: Greg Kroah-Hartman --- include/linux/kref.h | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) (limited to 'include/linux/kref.h') diff --git a/include/linux/kref.h b/include/linux/kref.h index d66c88a3b48c..abc0120b09b7 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -15,8 +15,8 @@ #ifndef _KREF_H_ #define _KREF_H_ -#include -#include +#include +#include struct kref { atomic_t refcount; @@ -48,7 +48,10 @@ static inline void kref_get(struct kref *kref) * @release: pointer to the function that will clean up the object when the * last reference to the object is released. * This pointer is required, and it is not acceptable to pass kfree - * in as this function. + * in as this function. If the caller does pass kfree to this + * function, you will be publicly mocked mercilessly by the kref + * maintainer, and anyone else who happens to notice it. You have + * been warned. * * Subtract @count from the refcount, and if 0, call release(). * Return 1 if the object was removed, otherwise return 0. Beware, if this @@ -60,7 +63,6 @@ static inline int kref_sub(struct kref *kref, unsigned int count, void (*release)(struct kref *kref)) { WARN_ON(release == NULL); - WARN_ON(release == (void (*)(struct kref *))kfree); if (atomic_sub_and_test((int) count, &kref->refcount)) { release(kref); @@ -75,7 +77,10 @@ static inline int kref_sub(struct kref *kref, unsigned int count, * @release: pointer to the function that will clean up the object when the * last reference to the object is released. * This pointer is required, and it is not acceptable to pass kfree - * in as this function. + * in as this function. If the caller does pass kfree to this + * function, you will be publicly mocked mercilessly by the kref + * maintainer, and anyone else who happens to notice it. You have + * been warned. * * Decrement the refcount, and if 0, call release(). * Return 1 if the object was removed, otherwise return 0. Beware, if this -- cgit