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authorLinus Torvalds <torvalds@linux-foundation.org>2018-03-19 14:48:35 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-03-19 14:48:35 -0700
commit0d707a2f24c4a962313cffc980e2d74df460e45a (patch)
tree3db3487e147c1c6482edfe3ae22f0c8ec0857978 /include
parentefac2483e8f289cd879e750075e63a9d16897e65 (diff)
parentb3a5d111994450909158929560906f2c1c6c1d85 (diff)
downloadlinux-0d707a2f24c4a962313cffc980e2d74df460e45a.tar.bz2
Merge branch 'for-4.16-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu
Pull percpu fixes from Tejun Heo: "Late percpu pull request for v4.16-rc6. - percpu allocator pool replenishing no longer triggers OOM or warning messages. Also, the alloc interface now understands __GFP_NORETRY and __GFP_NOWARN. This is to allow avoiding OOMs from userland triggered actions like bpf map creation. Also added cond_resched() in alloc loop. - perpcu allocation now can be interrupted by kill sigs to avoid deadlocking OOM killer. - Added Dennis Zhou as a co-maintainer. He has rewritten the area map allocator, understands most of the code base and has been responsive for all bug reports" * 'for-4.16-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu: percpu_ref: Update doc to dissuade users from depending on internal RCU grace periods mm: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn() percpu: include linux/sched.h for cond_resched() percpu: add a schedule point in pcpu_balance_workfn() percpu: allow select gfp to be passed to underlying allocators percpu: add __GFP_NORETRY semantics to the percpu balancing path percpu: match chunk allocator declarations with definitions percpu: add Dennis Zhou as a percpu co-maintainer
Diffstat (limited to 'include')
-rw-r--r--include/linux/percpu-refcount.h18
1 files changed, 12 insertions, 6 deletions
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 864d167a1073..009cdf3d65b6 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -30,10 +30,14 @@
* calls io_destroy() or the process exits.
*
* In the aio code, kill_ioctx() is called when we wish to destroy a kioctx; it
- * calls percpu_ref_kill(), then hlist_del_rcu() and synchronize_rcu() to remove
- * the kioctx from the proccess's list of kioctxs - after that, there can't be
- * any new users of the kioctx (from lookup_ioctx()) and it's then safe to drop
- * the initial ref with percpu_ref_put().
+ * removes the kioctx from the proccess's table of kioctxs and kills percpu_ref.
+ * After that, there can't be any new users of the kioctx (from lookup_ioctx())
+ * and it's then safe to drop the initial ref with percpu_ref_put().
+ *
+ * Note that the free path, free_ioctx(), needs to go through explicit call_rcu()
+ * to synchronize with RCU protected lookup_ioctx(). percpu_ref operations don't
+ * imply RCU grace periods of any kind and if a user wants to combine percpu_ref
+ * with RCU protection, it must be done explicitly.
*
* Code that does a two stage shutdown like this often needs some kind of
* explicit synchronization to ensure the initial refcount can only be dropped
@@ -113,8 +117,10 @@ void percpu_ref_reinit(struct percpu_ref *ref);
* Must be used to drop the initial ref on a percpu refcount; must be called
* precisely once before shutdown.
*
- * Puts @ref in non percpu mode, then does a call_rcu() before gathering up the
- * percpu counters and dropping the initial ref.
+ * Switches @ref into atomic mode before gathering up the percpu counters
+ * and dropping the initial ref.
+ *
+ * There are no implied RCU grace periods between kill and release.
*/
static inline void percpu_ref_kill(struct percpu_ref *ref)
{