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Subject: Re: Regression in 4.6.0-git - bisected to commit dd254f5a382c
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From: Matthew McClintock <mmcclint@codeaurora.org>
In-Reply-To: <20160525011036.GB14480@ZenIV.linux.org.uk>
Date: Tue, 24 May 2016 20:20:46 -0500
Cc: Larry Finger <Larry.Finger@lwfinger.net>,
        LKML <linux-kernel@vger.kernel.org>
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References: <57437683.30008@lwfinger.net> <20160524001854.GW14480@ZenIV.linux.org.uk> <57447CE1.9020207@lwfinger.net> <6E57F7A4-59B0-46EA-9FFF-D0A4BA2D8E51@codeaurora.org> <5744A899.70503@lwfinger.net> <3988EB49-F17D-452B-A1AD-F202265B1BCA@codeaurora.org> <5744AD31.4090808@lwfinger.net> <2D6D38D9-FE06-4115-8FB2-48CB2FB19809@codeaurora.org> <20160524234133.GA14480@ZenIV.linux.org.uk> <1CDF0CFA-CCD2-440A-B956-2787BD8F2C4F@codeaurora.org> <20160525011036.GB14480@ZenIV.linux.org.uk>
To: Al Viro <viro@ZenIV.linux.org.uk>
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> On May 24, 2016, at 8:10 PM, Al Viro <viro@ZenIV.linux.org.uk> wrote:
> 
> Slap the WARN_ON(!size); in the very beginning of iov_iter_advance(), see
> where it's triggered...

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 28cb431..d89e154 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -488,6 +488,7 @@ EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);

 void iov_iter_advance(struct iov_iter *i, size_t size)
 {
+       WARN_ON(!size);
        iterate_and_advance(i, size, v, 0, 0, 0)
 }
 EXPORT_SYMBOL(iov_iter_advance);

[    1.359869] This architecture does not have kernel memory protection.
init started: BusyBox v1.24.1 ()
starting pid 78, tty '': '/etc/init.d/rcS'
[    1.435863] random: udevadm urandom read with 0 bits of entropy available
[    1.448116] ------------[ cut here ]------------
[    1.448193] WARNING: CPU: 1 PID: 88 at lib/iov_iter.c:491 iov_iter_advance+0xf0/0x1b8
[    1.451973] Modules linked in:
[    1.462753] CPU: 1 PID: 88 Comm: udevd Not tainted 4.6.0 #195
[    1.462793] Hardware name: Qualcomm (Flattened Device Tree)
[    1.468346] [<c021a978>] (unwind_backtrace) from [<c02158a8>] (show_stack+0x20/0x24)
[    1.473713] [<c02158a8>] (show_stack) from [<c044f310>] (dump_stack+0x90/0xa4)
[    1.481701] [<c044f310>] (dump_stack) from [<c0228130>] (__warn+0xf8/0x110)
[    1.488727] [<c0228130>] (__warn) from [<c0228218>] (warn_slowpath_null+0x30/0x38)
[    1.495588] [<c0228218>] (warn_slowpath_null) from [<c04607e8>] (iov_iter_advance+0xf0/0x1b8)
[    1.503244] [<c04607e8>] (iov_iter_advance) from [<c034114c>] (do_readv_writev+0x2d0/0x370)
[    1.511827] [<c034114c>] (do_readv_writev) from [<c034123c>] (vfs_readv+0x50/0x68)
[    1.519983] [<c034123c>] (vfs_readv) from [<c03412b0>] (do_readv+0x5c/0xb8)
[    1.527621] [<c03412b0>] (do_readv) from [<c0341f18>] (SyS_readv+0x1c/0x20)
[    1.534485] [<c0341f18>] (SyS_readv) from [<c0210f80>] (ret_fast_syscall+0x0/0x3c)
[    1.541556] ---[ end trace eef892a602dbe329 ]---