From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELsQdcQp95czoLDRI2FkE38/+lB6UHhmJAjQ99ayxmH00OAGqXAgvf4t/+uDnqrBzwpBjESg ARC-Seal: i=1; a=rsa-sha256; t=1521484093; cv=none; d=google.com; s=arc-20160816; b=hx44QnXMmh1gU9It5Jz4tBOS2qdWaQTO+5kqB/g3wlvTQO4wNTXeN+Vfx/F3tPfpUM XjT807XxT7ucoiQNE//wo7ddrHnk9B9dkg+/BSsFObaEy9bS363MBh0rve58jNbP+Gg7 gLudZ355Dh3FzT9Wc11CBpeAzxcOewOfT0w0J92srFmzd3jCHG8Owo/0Su6GOqixrccW joB5yw3J93HukBToX95T7hfb0PHKogYH3BU2bl2B5M06IGsMGNfbxy3p+AgNh58vloPJ qhEnqViO6zSqN9AybO9k30pnCXE7wFdiz9Fexts88lChZ+/J3KJ7guCTbt61oMJEsAL7 b7CQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=8FCd8tKUeK8yAC+58onESIWJhTjEqtrEI8ZB7pfjklk=; b=DpdffKNPvL2xFNxvVxIEVR0Bex73FIF2XDVi0qIIQ5/wFsmiylRRGHjPGxehIugBwW /AYpqyGyoDKwy9V05n2tMoG8ytAC1pu5emqDHX4Ej6KUiqImSq8jOeBLPmwcuam+pVZP xoV2gCkaICIIK3K+oPMG/loM+7gQle+6ZR8MmaNgYtWm1T3sVaz7+7/a7iLTfnUCA0HE gQz4gmC7FY6F9QHaQxmsdtPlrWwtdpPl9EHQRWhZ7XplXxT1XoIjJj/Ki7VUjk9iGE7B dOcK+Z1/DASmqcjunmVKViVg40kijdz0Qb6bWeNeISK58XC3oDA2ZB1tMc9fdIbcnUDz l8hQ== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tejun Heo , Jann Horn , Kent Overstreet , Linus Torvalds Subject: [PATCH 4.9 230/241] fs/aio: Add explicit RCU grace period when freeing kioctx Date: Mon, 19 Mar 2018 19:08:15 +0100 Message-Id: <20180319180800.691401226@linuxfoundation.org> X-Mailer: git-send-email 2.16.2 In-Reply-To: <20180319180751.172155436@linuxfoundation.org> References: <20180319180751.172155436@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1595390653676229913?= X-GMAIL-MSGID: =?utf-8?q?1595391705216288864?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tejun Heo 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 Reported-by: Jann Horn Fixes: e34ecee2ae79 ("aio: Fix a trinity splat") Cc: Kent Overstreet Cc: Linus Torvalds Cc: stable@vger.kernel.org # v3.13+ Signed-off-by: Greg Kroah-Hartman --- 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 @@ -581,6 +582,12 @@ 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); @@ -594,6 +601,14 @@ 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); @@ -602,8 +617,8 @@ 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); } /* @@ -825,7 +840,7 @@ 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); /*