Merge tag 'for-linus-20170825' of git://git.infradead.org/linux-mtd

[mirror_ubuntu-artful-kernel.git] / include / linux / cpuset.h

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 119a3f9604b0d90b499bdbd6627d30fbc936469b..898cfe2eeb420ab8bf7201bf4b01dd315bdb265b 100644 (file)
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -18,6 +18,19 @@
 
 #ifdef CONFIG_CPUSETS
 
+/*
+ * Static branch rewrites can happen in an arbitrary order for a given
+ * key. In code paths where we need to loop with read_mems_allowed_begin() and
+ * read_mems_allowed_retry() to get a consistent view of mems_allowed, we need
+ * to ensure that begin() always gets rewritten before retry() in the
+ * disabled -> enabled transition. If not, then if local irqs are disabled
+ * around the loop, we can deadlock since retry() would always be
+ * comparing the latest value of the mems_allowed seqcount against 0 as
+ * begin() still would see cpusets_enabled() as false. The enabled -> disabled
+ * transition should happen in reverse order for the same reasons (want to stop
+ * looking at real value of mems_allowed.sequence in retry() first).
+ */
+extern struct static_key_false cpusets_pre_enable_key;
 extern struct static_key_false cpusets_enabled_key;
 static inline bool cpusets_enabled(void)
 {
@@ -32,12 +45,14 @@ static inline int nr_cpusets(void)
 
 static inline void cpuset_inc(void)
 {
+       static_branch_inc(&cpusets_pre_enable_key);
        static_branch_inc(&cpusets_enabled_key);
 }
 
 static inline void cpuset_dec(void)
 {
        static_branch_dec(&cpusets_enabled_key);
+       static_branch_dec(&cpusets_pre_enable_key);
 }
 
 extern int cpuset_init(void);
@@ -115,7 +130,7 @@ extern void cpuset_print_current_mems_allowed(void);
  */
 static inline unsigned int read_mems_allowed_begin(void)
 {
-       if (!cpusets_enabled())
+       if (!static_branch_unlikely(&cpusets_pre_enable_key))
                return 0;
 
        return read_seqcount_begin(&current->mems_allowed_seq);
@@ -129,7 +144,7 @@ static inline unsigned int read_mems_allowed_begin(void)
  */
 static inline bool read_mems_allowed_retry(unsigned int seq)
 {
-       if (!cpusets_enabled())
+       if (!static_branch_unlikely(&cpusets_enabled_key))
                return false;
 
        return read_seqcount_retry(&current->mems_allowed_seq, seq);