proc/stat: convert to single_open_size()

These two patches are supposed to "fix" failed order-4 memory allocations
which have been observed when reading /proc/stat.  The problem has been
observed on s390 as well as on x86.

To address the problem change the seq_file memory allocations to fallback
to use vmalloc, so that allocations also work if memory is fragmented.

This approach seems to be simpler and less intrusive than changing
/proc/stat to use an interator.  Also it "fixes" other users as well,
which use seq_file's single_open() interface.

This patch (of 2):

Use seq_file's single_open_size() to preallocate a buffer that is large
enough to hold the whole output, instead of open coding it.  Also
calculate the requested size using the number of online cpus instead of
possible cpus, since the size of the output only depends on the number of
online cpus.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Ian Kent <raven@themaw.net>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Thorsten Diehl <thorsten.diehl@de.ibm.com>
Cc: Andrea Righi <andrea@betterlinux.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Stefan Bader <stefan.bader@canonical.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 9d231e9e5f0ef48cd7ef372437d85fbf9b8cbc2e..bf2d03f8fd3e1ae6fec98e5bd7f81bb1410bf6dd 100644 (file)
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -184,29 +184,11 @@ static int show_stat(struct seq_file *p, void *v)
 
 static int stat_open(struct inode *inode, struct file *file)
 {
-       size_t size = 1024 + 128 * num_possible_cpus();
-       char *buf;
-       struct seq_file *m;
-       int res;
+       size_t size = 1024 + 128 * num_online_cpus();
 
        /* minimum size to display an interrupt count : 2 bytes */
        size += 2 * nr_irqs;
-
-       /* don't ask for more than the kmalloc() max size */
-       if (size > KMALLOC_MAX_SIZE)
-               size = KMALLOC_MAX_SIZE;
-       buf = kmalloc(size, GFP_KERNEL);
-       if (!buf)
-               return -ENOMEM;
-
-       res = single_open(file, show_stat, NULL);
-       if (!res) {
-               m = file->private_data;
-               m->buf = buf;
-               m->size = ksize(buf);
-       } else
-               kfree(buf);
-       return res;
+       return single_open_size(file, show_stat, NULL, size);
 }
 
 static const struct file_operations proc_stat_operations = {