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Sun, 23 Feb 2020 05:15:16 -0800 Received: from MTKMBS01N2.mediatek.inc (172.21.101.79) by MTKMBS62DR.mediatek.inc (172.29.94.18) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Sun, 23 Feb 2020 05:15:13 -0800 Received: from mtkcas09.mediatek.inc (172.21.101.178) by mtkmbs01n2.mediatek.inc (172.21.101.79) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Sun, 23 Feb 2020 21:11:02 +0800 Received: from [172.21.77.33] (172.21.77.33) by mtkcas09.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Sun, 23 Feb 2020 21:14:50 +0800 Message-ID: <1582463706.19053.32.camel@mtkswgap22> Subject: Re: [PATCH] lib: iov_iter.c: fix a possible calculation error on remaining bytes From: Macpaul Lin To: Al Viro Date: Sun, 23 Feb 2020 21:15:06 +0800 In-Reply-To: <20200218124142.GJ23230@ZenIV.linux.org.uk> References: <1582011672-17189-1-git-send-email-macpaul.lin@mediatek.com> <20200218124142.GJ23230@ZenIV.linux.org.uk> X-Mailer: Evolution 3.2.3-0ubuntu6 MIME-Version: 1.0 X-TM-SNTS-SMTP: D743D5FFED43F9BC952FE27FF4BE8AE9BAFC6F359885D5FD278658A4DF9A560E2000:8 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200223_051519_000657_00CF5B30 X-CRM114-Status: GOOD ( 23.12 ) X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sasha Levin , Shen Jing , CC Hwang , Mediatek WSD Upstream , Jerry Zhang , linux-usb@vger.kernel.org, Loda Chou , linux-kernel@vger.kernel.org, Andrzej Pietrasiewicz , John Stultz , Vincent Pelletier , Matthias Brugger , linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org On Tue, 2020-02-18 at 12:41 +0000, Al Viro wrote: > On Tue, Feb 18, 2020 at 03:41:12PM +0800, Macpaul Lin wrote: > > This issue was found when adbd trying to open functionfs with AIO mode. > > Usually, we need to set "setprop sys.usb.ffs.aio_compat 0" to enable > > adbd with AIO mode on Android. > > > > When adbd is opening functionfs, it will try to read 24 bytes at the > > fisrt read I/O control. If this reading has been failed, adbd will > > try to send FUNCTIONFS_CLEAR_HALT to functionfs. When adbd is in AIO > > mode, functionfs will be acted with asyncronized I/O path. After the > > successful read transfer has been completed by gadget hardware, the > > following series of functions will be called. > > ffs_epfile_async_io_complete() -> ffs_user_copy_worker() -> > > copy_to_iter() -> _copy_to_iter() -> copyout() -> > > iterate_and_advance() -> iterate_iovec() > > > > Adding debug trace to these functions, it has been found that in > > iterate_iovec(), the calculation result of n will be turned into zero. > > n = wanted - n; /* 0 == n = 24 - 24; */ > > Which causes copyout() won't copy data to userspace since the length > > to be copied "v.iov_len" will be zero, which isn't correct. This also > > leads ffs_copy_to_iter() always return -EFAULT. Finally adbd cannot > > open functionfs and send FUNCTIONFS_CLEAR_HALT. > > > > Signed-off-by: Macpaul Lin > > --- > > lib/iov_iter.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > > index fb29c02c6a3c..f9334144e259 100644 > > --- a/lib/iov_iter.c > > +++ b/lib/iov_iter.c > > @@ -36,7 +36,8 @@ > > skip = __v.iov_len; \ > > n -= __v.iov_len; \ > > } \ > > - n = wanted - n; \ > > + if (n != wanted) \ > > + n = wanted - n; \ > > } > > First of all, nothing in that line can possibly *cause* > copyout() to do anything - it's after the calls of step. What's > more, this changes behaviour only when wanted would've been equal to > n, doesn't it? Which translates into "no decrements of n have > happened at all", i.e. "nothing has been copied". IOW, it's > a consequence of no copyout, not the cause of such. You can > make copy_to_iter() lie and pretend if has copied everything > when it has copied nothing, but that won't change the underlying > bug. > > So I'm afraid your debugging is not finished - you > still need to find out what causes the copyout failures and/or > BS iov_iter padded by caller. Thanks for your explanation. After these days, I've found this issue only happened on arm 64-bit system, while arm 32-bit system works well. After more debugging, it looks like arm 64 tagged ABI related issue. I've update a new patch here: usb: gadget: f_fs: try to fix AIO issue under ARM 64 bit TAGGED mode https://lkml.org/lkml/2020/2/23/16. Thanks. Macpaul Lin. _______________________________________________ Linux-mediatek mailing list Linux-mediatek@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-mediatek