linux-kernel - Re: [PATCH 1/6] seq_file: add seq_read

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Message-ID: <20201114061934.GA658@Ryzen-9-3900X.localdomain>
Date:   Fri, 13 Nov 2020 23:19:34 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, linux-hyperv@...r.kernel.org
Subject: Re: [PATCH 1/6] seq_file: add seq_read_iter

On Sat, Nov 14, 2020 at 05:50:48AM +0000, Al Viro wrote:
> On Fri, Nov 13, 2020 at 09:14:20PM -0700, Nathan Chancellor wrote:
> 
> > Unfortunately that patch does not solve my issue. Is there any other
> > debugging I should add?
> 
> Hmm...  I wonder which file it is; how about
> 		if (WARN_ON(!iovec.iov_len))
> 			printk(KERN_ERR "odd readv on %pd4\n", file);
> in the loop in fs/read_write.c:do_loop_readv_writev()?

Assuming you mean this?

diff --git a/fs/read_write.c b/fs/read_write.c
index 75f764b43418..91dc07074a3f 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -757,6 +757,9 @@ static ssize_t do_loop_readv_writev(struct file *filp, struct iov_iter *iter,
 		struct iovec iovec = iov_iter_iovec(iter);
 		ssize_t nr;
 
+		if (WARN_ON(!iovec.iov_len))
+			printk(KERN_ERR "odd readv on %pd4\n", filp);
+
 		if (type == READ) {
 			nr = filp->f_op->read(filp, iovec.iov_base,
 					      iovec.iov_len, ppos);

---

Assuming so, I have attached the output both with and without the
WARN_ON. Looks like mountinfo is what is causing the error?

Cheers,
Nathan

View attachment "dmesg_warn_on.txt" of type "text/plain" (272119 bytes)

View attachment "dmesg_err.txt" of type "text/plain" (8631 bytes)