NFS 4.2 client support broken on 5.10.5

[Kurt Garloff <kurt@garloff.de>]

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Hi Neil, Anna, Trond,

compiling a kernel, I suddenly started getting errors from objtool orc.
(This first occurs on init/main.o.)

I looked at all kind of things, before I noticed that this was not a
toolchain issue (gcc-10.2.1 self compiled), gcc plugins (I use
structleak and stackleak) nor an issue with objtool or libelf,
but that there was an -EIO error.

The kernel tree is on an NFS share, and I run 5.10.5 client kernel
against the kernel NFS (4.2) server, running a 5.10.3 kernel.

The issue does NOT occur on a 5.10.3 client kernel, but is easily
reproducible on 5.10.5. Note that 5.10.5 on a local file system or
against an NFSv3 server does not show the issue.

Test program that reproduces this on the first pwrite64() is attached.
Note that the call to ftruncate() is required to make the problem happen.

I could go on bisecting this to a particular patch, but you'll
probably be able to see right away what's wrong.

Best,

-- 
Kurt Garloff <kurt@garloff.de>
Cologne, Germany


[-- Attachment #2: testpwrite.c --]
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/* testpwrite.c
 * reproduces issue on NFS 4.2 client on Linux 5.10.5
 * (c) Kurt Garloff <scs@garloff.de>, 1/2021
 * License: GNU GPL 2 or later 
 */

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <time.h>

#define MAXBUF 1048576
#define MAXSIZE (128*MAXBUF)
#define REP 16384

long randomwrite(int fd)
{
	void* buf = malloc(MAXBUF);
	long written = 0;
	int rep = REP;
	int ret;
	if (!buf) {
		perror("malloc");
		return -3;
	}

	memset(buf, 0, MAXBUF);
	while (--rep) {
#if MAXSIZE >= RAND_MAX
		loff_t offset = rand() * (MAXSIZE/RAND_MAX);
#else
		loff_t offset = rand() / (RAND_MAX/MAXSIZE);
#endif
#if MAXBUF >= RAND_MAX
		size_t len = rand() * (MAXBUF/RAND_MAX);
#else
		size_t len = rand() / (RAND_MAX/MAXBUF);
#endif
		//ret = pread(fd, buf+len/4, len/2, offset);
		/* Slowly fill in some random non-0 values */
		*(int*)(buf + (len - len%8)) = rand();
		ret = pwrite(fd, buf, len, offset);
		if (ret < 0) {
			fprintf(stderr, "pwrite(%i,%p,%li,%li): ", fd, buf, len, offset);
			perror("");
			return -1;
		} else 
			written += ret;
	}
	return written;
}

int main(int argc, char *argv[])
{
	srand(time(0));
	int fd = open("testfile", O_RDWR|O_CREAT, S_IRUSR|S_IWUSR|S_IRGRP);
	if (fd <= 0) {
		perror("open(\"testfile\")");
		return 2;
	}
	ftruncate(fd, MAXSIZE);
	unlink("testfile");
	long rc = randomwrite(fd);
	close(fd);
	if (rc < 0)
		return -rc;
	printf("%li bytes written successfully\n", rc);
	return 0;
}