This is a note to let you know that I've just added the patch titled
fs/aio: Add explicit RCU grace period when freeing kioctx
to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fs-aio-add-explicit-rcu-grace-period-when-freeing-kioctx.patch
and it can be found in the queue-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From a6d7cff472eea87d96899a20fa718d2bab7109f3 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@xxxxxxxxxx>
Date: Wed, 14 Mar 2018 12:10:17 -0700
Subject: fs/aio: Add explicit RCU grace period when freeing kioctx
From: Tejun Heo <tj@xxxxxxxxxx>
commit a6d7cff472eea87d96899a20fa718d2bab7109f3 upstream.
While fixing refcounting, e34ecee2ae79 ("aio: Fix a trinity splat")
incorrectly removed explicit RCU grace period before freeing kioctx.
The intention seems to be depending on the internal RCU grace periods
of percpu_ref; however, percpu_ref uses a different flavor of RCU,
sched-RCU. This can lead to kioctx being freed while RCU read
protected dereferences are still in progress.
Fix it by updating free_ioctx() to go through call_rcu() explicitly.
v2: Comment added to explain double bouncing.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: Jann Horn <jannh@xxxxxxxxxx>
Fixes: e34ecee2ae79 ("aio: Fix a trinity splat")
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v3.13+
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/aio.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -110,7 +110,8 @@ struct kioctx {
struct page **ring_pages;
long nr_pages;
- struct work_struct free_work;
+ struct rcu_head free_rcu;
+ struct work_struct free_work; /* see free_ioctx() */
/*
* signals when all in-flight requests are done
@@ -505,6 +506,12 @@ static int kiocb_cancel(struct kiocb *ki
return cancel(kiocb);
}
+/*
+ * free_ioctx() should be RCU delayed to synchronize against the RCU
+ * protected lookup_ioctx() and also needs process context to call
+ * aio_free_ring(), so the double bouncing through kioctx->free_rcu and
+ * ->free_work.
+ */
static void free_ioctx(struct work_struct *work)
{
struct kioctx *ctx = container_of(work, struct kioctx, free_work);
@@ -518,6 +525,14 @@ static void free_ioctx(struct work_struc
kmem_cache_free(kioctx_cachep, ctx);
}
+static void free_ioctx_rcufn(struct rcu_head *head)
+{
+ struct kioctx *ctx = container_of(head, struct kioctx, free_rcu);
+
+ INIT_WORK(&ctx->free_work, free_ioctx);
+ schedule_work(&ctx->free_work);
+}
+
static void free_ioctx_reqs(struct percpu_ref *ref)
{
struct kioctx *ctx = container_of(ref, struct kioctx, reqs);
@@ -526,8 +541,8 @@ static void free_ioctx_reqs(struct percp
if (ctx->requests_done)
complete(ctx->requests_done);
- INIT_WORK(&ctx->free_work, free_ioctx);
- schedule_work(&ctx->free_work);
+ /* Synchronize against RCU protected table->table[] dereferences */
+ call_rcu(&ctx->free_rcu, free_ioctx_rcufn);
}
/*
@@ -749,7 +764,7 @@ static int kill_ioctx(struct mm_struct *
table->table[ctx->id] = NULL;
spin_unlock(&mm->ioctx_lock);
- /* percpu_ref_kill() will do the necessary call_rcu() */
+ /* free_ioctx_reqs() will do the necessary RCU synchronization */
wake_up_all(&ctx->wait);
/*
Patches currently in stable-queue which might be from tj@xxxxxxxxxx are
queue-3.18/fs-aio-add-explicit-rcu-grace-period-when-freeing-kioctx.patch
queue-3.18/fs-aio-use-rcu-accessors-for-kioctx_table-table.patch