From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6650EFBE8 for ; Thu, 1 Jun 2023 13:25:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E74DDC433D2; Thu, 1 Jun 2023 13:25:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1685625921; bh=F6e+tRtPck4CiqDKOP1ijt0erdJztUWmRMHwr4X4fXo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dfyI0Jzp3k+nr58HF+0L97LVR5VWWo4IWttluOqZj1Eoql4GLNq99GzHth4YoutZ+ 9uelo6MB1vhokPHZfdrvDch+N/mjb1DfpEL2pYDzSCMdgbDGv6HLM8f4upbOXUvguo HOJ/EVLvWqiE0uoX6e7nn2giHBSI5Lguhx7+OePM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Liam Howlett , Suren Baghdasaryan , Carlos Llamas Subject: [PATCH 5.15 39/42] binder: add lockless binder_alloc_(set|get)_vma() Date: Thu, 1 Jun 2023 14:21:26 +0100 Message-Id: <20230601131938.459836957@linuxfoundation.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230601131936.699199833@linuxfoundation.org> References: <20230601131936.699199833@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Carlos Llamas commit 0fa53349c3acba0239369ba4cd133740a408d246 upstream. Bring back the original lockless design in binder_alloc to determine whether the buffer setup has been completed by the ->mmap() handler. However, this time use smp_load_acquire() and smp_store_release() to wrap all the ordering in a single macro call. Also, add comments to make it evident that binder uses alloc->vma to determine when the binder_alloc has been fully initialized. In these scenarios acquiring the mmap_lock is not required. Fixes: a43cfc87caaf ("android: binder: stop saving a pointer to the VMA") Cc: Liam Howlett Cc: Suren Baghdasaryan Cc: stable@vger.kernel.org Signed-off-by: Carlos Llamas Link: https://lore.kernel.org/r/20230502201220.1756319-3-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman [cmllamas: fixed minor merge conflict in binder_alloc_set_vma()] Signed-off-by: Carlos Llamas Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder_alloc.c | 22 +++++++--------------- 1 file changed, 7 insertions(+), 15 deletions(-) --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -309,29 +309,18 @@ err_no_vma: return vma ? -ENOMEM : -ESRCH; } - static inline void binder_alloc_set_vma(struct binder_alloc *alloc, struct vm_area_struct *vma) { - /* - * If we see alloc->vma is not NULL, buffer data structures set up - * completely. Look at smp_rmb side binder_alloc_get_vma. - */ - smp_wmb(); - alloc->vma = vma; + /* pairs with smp_load_acquire in binder_alloc_get_vma() */ + smp_store_release(&alloc->vma, vma); } static inline struct vm_area_struct *binder_alloc_get_vma( struct binder_alloc *alloc) { - struct vm_area_struct *vma = NULL; - - if (alloc->vma) { - /* Look at description in binder_alloc_set_vma */ - smp_rmb(); - vma = alloc->vma; - } - return vma; + /* pairs with smp_store_release in binder_alloc_set_vma() */ + return smp_load_acquire(&alloc->vma); } static bool debug_low_async_space_locked(struct binder_alloc *alloc, int pid) @@ -394,6 +383,7 @@ static struct binder_buffer *binder_allo size_t size, data_offsets_size; int ret; + /* Check binder_alloc is fully initialized */ if (!binder_alloc_get_vma(alloc)) { binder_alloc_debug(BINDER_DEBUG_USER_ERROR, "%d: binder_alloc_buf, no vma\n", @@ -789,6 +779,8 @@ int binder_alloc_mmap_handler(struct bin buffer->free = 1; binder_insert_free_buffer(alloc, buffer); alloc->free_async_space = alloc->buffer_size / 2; + + /* Signal binder_alloc is fully initialized */ binder_alloc_set_vma(alloc, vma); return 0;