linux-kernel - linux-next: build failure after merge of the block tree

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Date:   Wed, 28 Jun 2017 18:04:56 +1000
From:   Stephen Rothwell <sfr@...b.auug.org.au>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        PowerPC <linuxppc-dev@...ts.ozlabs.org>
Subject: linux-next: build failure after merge of the block tree

Hi Jens,

After merging the block tree, today's linux-next build (powerpc
allnoconfig) failed like this:

fs/fcntl.o: In function `do_fcntl': 
fcntl.c:(.text+0x6d4): undefined reference to `__get_user_bad'
fcntl.c:(.text+0x730): undefined reference to `__get_user_bad'

Probably caused by commit

  c75b1d9421f8 ("fs: add fcntl() interface for setting/getting write life time hints")

On powerpc (at least) you cannot use get_user() to fetch anything larger
than "unsigned long" i.e. 32 bits on 32 bit powerpc.

This has been discussed before (and, I think, a fix attempted).

For now I have applied the following patch:

From: Stephen Rothwell <sfr@...b.auug.org.au>
Date: Wed, 28 Jun 2017 17:50:31 +1000
Subject: [PATCH] fs: don't read an enum directly from a u64 __user *

Signed-off-by: Stephen Rothwell <sfr@...b.auug.org.au>
---
 fs/fcntl.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 24e233c75a33..19825eb7c40d 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -277,6 +277,7 @@ static long fcntl_rw_hint(struct file *file, unsigned int cmd,
 {
 	struct inode *inode = file_inode(file);
 	u64 *argp = (u64 __user *)arg;
+	u64 h;
 	enum rw_hint hint;
 
 	switch (cmd) {
@@ -285,8 +286,9 @@ static long fcntl_rw_hint(struct file *file, unsigned int cmd,
 			return -EFAULT;
 		return 0;
 	case F_SET_FILE_RW_HINT:
-		if (get_user(hint, argp))
+		if (copy_from_user(&h, argp, sizeof(h)))
 			return -EFAULT;
+		hint = (enum rw_hint)h;
 		if (!rw_hint_valid(hint))
 			return -EINVAL;
 
@@ -299,8 +301,9 @@ static long fcntl_rw_hint(struct file *file, unsigned int cmd,
 			return -EFAULT;
 		return 0;
 	case F_SET_RW_HINT:
-		if (get_user(hint, argp))
+		if (copy_from_user(&h, argp, sizeof(h)))
 			return -EFAULT;
+		hint = (enum rw_hint)h;
 		if (!rw_hint_valid(hint))
 			return -EINVAL;
 
-- 
2.11.0

-- 
Cheers,
Stephen Rothwell