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authorTejun Heo <tj@kernel.org>2018-03-14 12:10:17 -0700
committerTejun Heo <tj@kernel.org>2018-03-14 12:10:17 -0700
commita6d7cff472eea87d96899a20fa718d2bab7109f3 (patch)
treeeb61b607a6fb3b77781c3e526ca33e0f885eb8b1 /fs
parent3032f8c504d2b15d58e4c96060a96b47e215573c (diff)
fs/aio: Add explicit RCU grace period when freeing kioctx
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@kernel.org> Reported-by: Jann Horn <jannh@google.com> Fixes: e34ecee2ae79 ("aio: Fix a trinity splat") Cc: Kent Overstreet <kent.overstreet@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: stable@vger.kernel.org # v3.13+
Diffstat (limited to 'fs')
-rw-r--r--fs/aio.c23
1 files changed, 19 insertions, 4 deletions
diff --git a/fs/aio.c b/fs/aio.c
index a062d75109cb..eb2e0cfbe2d2 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -115,7 +115,8 @@ 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
@@ -588,6 +589,12 @@ static int kiocb_cancel(struct aio_kiocb *kiocb)
return cancel(&kiocb->common);
}
+/*
+ * 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);
@@ -601,6 +608,14 @@ static void free_ioctx(struct work_struct *work)
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);
@@ -609,8 +624,8 @@ static void free_ioctx_reqs(struct percpu_ref *ref)
if (ctx->rq_wait && atomic_dec_and_test(&ctx->rq_wait->count))
complete(&ctx->rq_wait->comp);
- 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);
}
/*
@@ -838,7 +853,7 @@ static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
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);
/*