* [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup [not found] ` <20180314194515.1661824-1-tj@kernel.org> @ 2018-03-14 19:45 ` Tejun Heo 2018-03-26 14:54 ` Tejun Heo 0 siblings, 1 reply; 3+ messages in thread From: Tejun Heo @ 2018-03-14 19:45 UTC (permalink / raw) To: torvalds, jannh, paulmck, bcrl, viro, kent.overstreet Cc: security, linux-kernel, kernel-team, Tejun Heo, linux-mm hmm_devmem_find() requires rcu_read_lock_held() but there's nothing which actually uses the RCU protection. The only caller is hmm_devmem_pages_create() which already grabs the mutex and does superflous rcu_read_lock/unlock() around the function. This doesn't add anything and just adds to confusion. Remove the RCU protection and open-code the radix tree lookup. If this needs to become more sophisticated in the future, let's add them back when necessary. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: JA(C)rA'me Glisse <jglisse@redhat.com> Cc: linux-mm@kvack.org Cc: Linus Torvalds <torvalds@linux-foundation.org> --- Hello, JA(C)rA'me, how do you want to route this patch? If you prefer, I can route it together with other patches. Thanks. mm/hmm.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) diff --git a/mm/hmm.c b/mm/hmm.c index 320545b98..d4627c5 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -845,13 +845,6 @@ static void hmm_devmem_release(struct device *dev, void *data) hmm_devmem_radix_release(resource); } -static struct hmm_devmem *hmm_devmem_find(resource_size_t phys) -{ - WARN_ON_ONCE(!rcu_read_lock_held()); - - return radix_tree_lookup(&hmm_devmem_radix, phys >> PA_SECTION_SHIFT); -} - static int hmm_devmem_pages_create(struct hmm_devmem *devmem) { resource_size_t key, align_start, align_size, align_end; @@ -892,9 +885,8 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem) for (key = align_start; key <= align_end; key += PA_SECTION_SIZE) { struct hmm_devmem *dup; - rcu_read_lock(); - dup = hmm_devmem_find(key); - rcu_read_unlock(); + dup = radix_tree_lookup(&hmm_devmem_radix, + key >> PA_SECTION_SHIFT); if (dup) { dev_err(device, "%s: collides with mapping for %s\n", __func__, dev_name(dup->device)); -- 2.9.5 ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup 2018-03-14 19:45 ` [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup Tejun Heo @ 2018-03-26 14:54 ` Tejun Heo 2018-03-27 16:12 ` Jerome Glisse 0 siblings, 1 reply; 3+ messages in thread From: Tejun Heo @ 2018-03-26 14:54 UTC (permalink / raw) To: Andrew Morton Cc: security, linux-kernel, kernel-team, linux-mm, torvalds, jannh, paulmck, bcrl, viro, kent.overstreet Hello, Andrew. Do you mind picking up the following patch? I can't find a good tree to route this through. The raw patch can be found at https://marc.info/?l=linux-mm&m=152105674112496&q=raw Thank you very much. On Wed, Mar 14, 2018 at 12:45:11PM -0700, Tejun Heo wrote: > hmm_devmem_find() requires rcu_read_lock_held() but there's nothing > which actually uses the RCU protection. The only caller is > hmm_devmem_pages_create() which already grabs the mutex and does > superflous rcu_read_lock/unlock() around the function. > > This doesn't add anything and just adds to confusion. Remove the RCU > protection and open-code the radix tree lookup. If this needs to > become more sophisticated in the future, let's add them back when > necessary. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Reviewed-by: Jerome Glisse <jglisse@redhat.com> > Cc: linux-mm@kvack.org > Cc: Linus Torvalds <torvalds@linux-foundation.org> > --- > Hello, > > Jerome, how do you want to route this patch? If you prefer, I can > route it together with other patches. > > Thanks. > > mm/hmm.c | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/mm/hmm.c b/mm/hmm.c > index 320545b98..d4627c5 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -845,13 +845,6 @@ static void hmm_devmem_release(struct device *dev, void *data) > hmm_devmem_radix_release(resource); > } > > -static struct hmm_devmem *hmm_devmem_find(resource_size_t phys) > -{ > - WARN_ON_ONCE(!rcu_read_lock_held()); > - > - return radix_tree_lookup(&hmm_devmem_radix, phys >> PA_SECTION_SHIFT); > -} > - > static int hmm_devmem_pages_create(struct hmm_devmem *devmem) > { > resource_size_t key, align_start, align_size, align_end; > @@ -892,9 +885,8 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem) > for (key = align_start; key <= align_end; key += PA_SECTION_SIZE) { > struct hmm_devmem *dup; > > - rcu_read_lock(); > - dup = hmm_devmem_find(key); > - rcu_read_unlock(); > + dup = radix_tree_lookup(&hmm_devmem_radix, > + key >> PA_SECTION_SHIFT); > if (dup) { > dev_err(device, "%s: collides with mapping for %s\n", > __func__, dev_name(dup->device)); > -- > 2.9.5 > -- tejun ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup 2018-03-26 14:54 ` Tejun Heo @ 2018-03-27 16:12 ` Jerome Glisse 0 siblings, 0 replies; 3+ messages in thread From: Jerome Glisse @ 2018-03-27 16:12 UTC (permalink / raw) To: Tejun Heo Cc: Andrew Morton, security, linux-kernel, kernel-team, linux-mm, torvalds, jannh, paulmck, bcrl, viro, kent.overstreet On Mon, Mar 26, 2018 at 07:54:31AM -0700, Tejun Heo wrote: > Hello, Andrew. > > Do you mind picking up the following patch? I can't find a good tree > to route this through. The raw patch can be found at > > https://marc.info/?l=linux-mm&m=152105674112496&q=raw > > Thank you very much. I am fine with which ever route there is low probability of conflict when merging HMM through different tree. > > On Wed, Mar 14, 2018 at 12:45:11PM -0700, Tejun Heo wrote: > > hmm_devmem_find() requires rcu_read_lock_held() but there's nothing > > which actually uses the RCU protection. The only caller is > > hmm_devmem_pages_create() which already grabs the mutex and does > > superflous rcu_read_lock/unlock() around the function. > > > > This doesn't add anything and just adds to confusion. Remove the RCU > > protection and open-code the radix tree lookup. If this needs to > > become more sophisticated in the future, let's add them back when > > necessary. > > > > Signed-off-by: Tejun Heo <tj@kernel.org> > > Reviewed-by: Jerome Glisse <jglisse@redhat.com> > > Cc: linux-mm@kvack.org > > Cc: Linus Torvalds <torvalds@linux-foundation.org> > > --- > > Hello, > > > > Jerome, how do you want to route this patch? If you prefer, I can > > route it together with other patches. > > > > Thanks. > > > > mm/hmm.c | 12 ++---------- > > 1 file changed, 2 insertions(+), 10 deletions(-) > > > > diff --git a/mm/hmm.c b/mm/hmm.c > > index 320545b98..d4627c5 100644 > > --- a/mm/hmm.c > > +++ b/mm/hmm.c > > @@ -845,13 +845,6 @@ static void hmm_devmem_release(struct device *dev, void *data) > > hmm_devmem_radix_release(resource); > > } > > > > -static struct hmm_devmem *hmm_devmem_find(resource_size_t phys) > > -{ > > - WARN_ON_ONCE(!rcu_read_lock_held()); > > - > > - return radix_tree_lookup(&hmm_devmem_radix, phys >> PA_SECTION_SHIFT); > > -} > > - > > static int hmm_devmem_pages_create(struct hmm_devmem *devmem) > > { > > resource_size_t key, align_start, align_size, align_end; > > @@ -892,9 +885,8 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem) > > for (key = align_start; key <= align_end; key += PA_SECTION_SIZE) { > > struct hmm_devmem *dup; > > > > - rcu_read_lock(); > > - dup = hmm_devmem_find(key); > > - rcu_read_unlock(); > > + dup = radix_tree_lookup(&hmm_devmem_radix, > > + key >> PA_SECTION_SHIFT); > > if (dup) { > > dev_err(device, "%s: collides with mapping for %s\n", > > __func__, dev_name(dup->device)); > > -- > > 2.9.5 > > > > -- > tejun ^ permalink raw reply [flat|nested] 3+ messages in thread
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2018-03-14 19:45 ` [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup Tejun Heo
2018-03-26 14:54 ` Tejun Heo
2018-03-27 16:12 ` Jerome Glisse
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