| Message ID | 153910718919.7006.13400779039257185427.stgit@localhost.localdomain (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: Convert mem_cgroup_id::ref to refcount_t type | expand |
On Tue 09-10-18 20:46:56, Kirill Tkhai wrote: > This will allow to use generic refcount_t interfaces > to check counters overflow instead of currently existing > VM_BUG_ON(). The only difference after the patch is > VM_BUG_ON() may cause BUG(), while refcount_t fires > with WARN(). But this seems not to be significant here, > since such the problems are usually caught by syzbot > with panic-on-warn enabled. > > Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> Acked-by: Michal Hocko <mhocko@suse.com> > --- > include/linux/memcontrol.h | 2 +- > mm/memcontrol.c | 10 ++++------ > 2 files changed, 5 insertions(+), 7 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 4399cc3f00e4..7ab2120155a4 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -78,7 +78,7 @@ struct mem_cgroup_reclaim_cookie { > > struct mem_cgroup_id { > int id; > - atomic_t ref; > + refcount_t ref; > }; > > /* > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 7bebe2ddec05..aa728d5b3d72 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -4299,14 +4299,12 @@ static void mem_cgroup_id_remove(struct mem_cgroup *memcg) > > static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n) > { > - VM_BUG_ON(atomic_read(&memcg->id.ref) <= 0); > - atomic_add(n, &memcg->id.ref); > + refcount_add(n, &memcg->id.ref); > } > > static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n) > { > - VM_BUG_ON(atomic_read(&memcg->id.ref) < n); > - if (atomic_sub_and_test(n, &memcg->id.ref)) { > + if (refcount_sub_and_test(n, &memcg->id.ref)) { > mem_cgroup_id_remove(memcg); > > /* Memcg ID pins CSS */ > @@ -4523,7 +4521,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) > } > > /* Online state pins memcg ID, memcg ID pins CSS */ > - atomic_set(&memcg->id.ref, 1); > + refcount_set(&memcg->id.ref, 1); > css_get(css); > return 0; > } > @@ -6357,7 +6355,7 @@ subsys_initcall(mem_cgroup_init); > #ifdef CONFIG_MEMCG_SWAP > static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg) > { > - while (!atomic_inc_not_zero(&memcg->id.ref)) { > + while (!refcount_inc_not_zero(&memcg->id.ref)) { > /* > * The root cgroup cannot be destroyed, so it's refcount must > * always be >= 1.
Hi Kirill, On Tue, Oct 09, 2018 at 08:46:56PM +0300, Kirill Tkhai wrote: > This will allow to use generic refcount_t interfaces > to check counters overflow instead of currently existing > VM_BUG_ON(). The only difference after the patch is > VM_BUG_ON() may cause BUG(), while refcount_t fires > with WARN(). refcount_{sub_and_test,inc_not_zero}() are documented to provide "slightly" more relaxed ordering than their atomic_* counterpart, c.f., Documentation/core-api/refcount-vs-atomic.rst lib/refcount.c (inline comments) IIUC, this semantic change won't cause problems here (but please double-check? ;D ). Andrea >But this seems not to be significant here, > since such the problems are usually caught by syzbot > with panic-on-warn enabled. > > Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> > --- > include/linux/memcontrol.h | 2 +- > mm/memcontrol.c | 10 ++++------ > 2 files changed, 5 insertions(+), 7 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 4399cc3f00e4..7ab2120155a4 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -78,7 +78,7 @@ struct mem_cgroup_reclaim_cookie { > > struct mem_cgroup_id { > int id; > - atomic_t ref; > + refcount_t ref; > }; > > /* > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 7bebe2ddec05..aa728d5b3d72 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -4299,14 +4299,12 @@ static void mem_cgroup_id_remove(struct mem_cgroup *memcg) > > static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n) > { > - VM_BUG_ON(atomic_read(&memcg->id.ref) <= 0); > - atomic_add(n, &memcg->id.ref); > + refcount_add(n, &memcg->id.ref); > } > > static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n) > { > - VM_BUG_ON(atomic_read(&memcg->id.ref) < n); > - if (atomic_sub_and_test(n, &memcg->id.ref)) { > + if (refcount_sub_and_test(n, &memcg->id.ref)) { > mem_cgroup_id_remove(memcg); > > /* Memcg ID pins CSS */ > @@ -4523,7 +4521,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) > } > > /* Online state pins memcg ID, memcg ID pins CSS */ > - atomic_set(&memcg->id.ref, 1); > + refcount_set(&memcg->id.ref, 1); > css_get(css); > return 0; > } > @@ -6357,7 +6355,7 @@ subsys_initcall(mem_cgroup_init); > #ifdef CONFIG_MEMCG_SWAP > static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg) > { > - while (!atomic_inc_not_zero(&memcg->id.ref)) { > + while (!refcount_inc_not_zero(&memcg->id.ref)) { > /* > * The root cgroup cannot be destroyed, so it's refcount must > * always be >= 1. >
Hi, Andrea, On 16.10.2018 15:49, Andrea Parri wrote: > Hi Kirill, > > On Tue, Oct 09, 2018 at 08:46:56PM +0300, Kirill Tkhai wrote: >> This will allow to use generic refcount_t interfaces >> to check counters overflow instead of currently existing >> VM_BUG_ON(). The only difference after the patch is >> VM_BUG_ON() may cause BUG(), while refcount_t fires >> with WARN(). > > refcount_{sub_and_test,inc_not_zero}() are documented to provide > "slightly" more relaxed ordering than their atomic_* counterpart, > c.f., > > Documentation/core-api/refcount-vs-atomic.rst > lib/refcount.c (inline comments) > > IIUC, this semantic change won't cause problems here (but please > double-check? ;D ). I just don't see a place, where we may think about using a modification of struct mem_cgroup::id::ref as a memory barrier to order something, and all this looks safe for me. Kirill >> But this seems not to be significant here, >> since such the problems are usually caught by syzbot >> with panic-on-warn enabled. >> >> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> >> --- >> include/linux/memcontrol.h | 2 +- >> mm/memcontrol.c | 10 ++++------ >> 2 files changed, 5 insertions(+), 7 deletions(-) >> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >> index 4399cc3f00e4..7ab2120155a4 100644 >> --- a/include/linux/memcontrol.h >> +++ b/include/linux/memcontrol.h >> @@ -78,7 +78,7 @@ struct mem_cgroup_reclaim_cookie { >> >> struct mem_cgroup_id { >> int id; >> - atomic_t ref; >> + refcount_t ref; >> }; >> >> /* >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 7bebe2ddec05..aa728d5b3d72 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -4299,14 +4299,12 @@ static void mem_cgroup_id_remove(struct mem_cgroup *memcg) >> >> static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n) >> { >> - VM_BUG_ON(atomic_read(&memcg->id.ref) <= 0); >> - atomic_add(n, &memcg->id.ref); >> + refcount_add(n, &memcg->id.ref); >> } >> >> static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n) >> { >> - VM_BUG_ON(atomic_read(&memcg->id.ref) < n); >> - if (atomic_sub_and_test(n, &memcg->id.ref)) { >> + if (refcount_sub_and_test(n, &memcg->id.ref)) { >> mem_cgroup_id_remove(memcg); >> >> /* Memcg ID pins CSS */ >> @@ -4523,7 +4521,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) >> } >> >> /* Online state pins memcg ID, memcg ID pins CSS */ >> - atomic_set(&memcg->id.ref, 1); >> + refcount_set(&memcg->id.ref, 1); >> css_get(css); >> return 0; >> } >> @@ -6357,7 +6355,7 @@ subsys_initcall(mem_cgroup_init); >> #ifdef CONFIG_MEMCG_SWAP >> static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg) >> { >> - while (!atomic_inc_not_zero(&memcg->id.ref)) { >> + while (!refcount_inc_not_zero(&memcg->id.ref)) { >> /* >> * The root cgroup cannot be destroyed, so it's refcount must >> * always be >= 1. >>
On Tue 16-10-18 16:19:40, Kirill Tkhai wrote: > Hi, Andrea, > > On 16.10.2018 15:49, Andrea Parri wrote: > > Hi Kirill, > > > > On Tue, Oct 09, 2018 at 08:46:56PM +0300, Kirill Tkhai wrote: > >> This will allow to use generic refcount_t interfaces > >> to check counters overflow instead of currently existing > >> VM_BUG_ON(). The only difference after the patch is > >> VM_BUG_ON() may cause BUG(), while refcount_t fires > >> with WARN(). > > > > refcount_{sub_and_test,inc_not_zero}() are documented to provide > > "slightly" more relaxed ordering than their atomic_* counterpart, > > c.f., > > > > Documentation/core-api/refcount-vs-atomic.rst > > lib/refcount.c (inline comments) > > > > IIUC, this semantic change won't cause problems here (but please > > double-check? ;D ). > > I just don't see a place, where we may think about using a modification > of struct mem_cgroup::id::ref as a memory barrier to order something, > and all this looks safe for me. If there was any it would surely be unintentional. memcg->id.ref is a clear reference counter pattern for the id lifetime.
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 4399cc3f00e4..7ab2120155a4 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -78,7 +78,7 @@ struct mem_cgroup_reclaim_cookie { struct mem_cgroup_id { int id; - atomic_t ref; + refcount_t ref; }; /* diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 7bebe2ddec05..aa728d5b3d72 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4299,14 +4299,12 @@ static void mem_cgroup_id_remove(struct mem_cgroup *memcg) static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n) { - VM_BUG_ON(atomic_read(&memcg->id.ref) <= 0); - atomic_add(n, &memcg->id.ref); + refcount_add(n, &memcg->id.ref); } static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n) { - VM_BUG_ON(atomic_read(&memcg->id.ref) < n); - if (atomic_sub_and_test(n, &memcg->id.ref)) { + if (refcount_sub_and_test(n, &memcg->id.ref)) { mem_cgroup_id_remove(memcg); /* Memcg ID pins CSS */ @@ -4523,7 +4521,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) } /* Online state pins memcg ID, memcg ID pins CSS */ - atomic_set(&memcg->id.ref, 1); + refcount_set(&memcg->id.ref, 1); css_get(css); return 0; } @@ -6357,7 +6355,7 @@ subsys_initcall(mem_cgroup_init); #ifdef CONFIG_MEMCG_SWAP static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg) { - while (!atomic_inc_not_zero(&memcg->id.ref)) { + while (!refcount_inc_not_zero(&memcg->id.ref)) { /* * The root cgroup cannot be destroyed, so it's refcount must * always be >= 1.
This will allow to use generic refcount_t interfaces to check counters overflow instead of currently existing VM_BUG_ON(). The only difference after the patch is VM_BUG_ON() may cause BUG(), while refcount_t fires with WARN(). But this seems not to be significant here, since such the problems are usually caught by syzbot with panic-on-warn enabled. Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> --- include/linux/memcontrol.h | 2 +- mm/memcontrol.c | 10 ++++------ 2 files changed, 5 insertions(+), 7 deletions(-)