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 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
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-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From a6d7cff472eea87d96899a20fa718d2bab7109f3 Mon Sep 17 00:00:00 2001
From: Tejun Heo tj@kernel.org Date: Wed, 14 Mar 2018 12:10:17 -0700 Subject: fs/aio: Add explicit RCU grace period when freeing kioctx
From: Tejun Heo tj@kernel.org
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@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+ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/aio.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-)
--- 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 @@ -573,6 +574,12 @@ static int kiocb_cancel(struct aio_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); @@ -586,6 +593,14 @@ 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); @@ -594,8 +609,8 @@ static void free_ioctx_reqs(struct percp 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); }
/* @@ -817,7 +832,7 @@ 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@kernel.org are
queue-4.4/fs-aio-add-explicit-rcu-grace-period-when-freeing-kioctx.patch queue-4.4/fs-aio-use-rcu-accessors-for-kioctx_table-table.patch