[PATCH 3.12 108/142] fs/seq_file: fallback to vmalloc allocation

Jiri Slaby
2015-05-16T08:05:25Z

From: Heiko Carstens <heiko.carstens@de.ibm.com>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit 058504edd02667eef8fac9be27ab3ea74332e9b4 upstream.

There are a couple of seq_files which use the single_open() interface.
This interface requires that the whole output must fit into a single
buffer.

E.g. for /proc/stat allocation failures have been observed because an
order-4 memory allocation failed due to memory fragmentation. In such
situations reading /proc/stat is not possible anymore.

Therefore change the seq_file code to fallback to vmalloc allocations
which will usually result in a couple of order-0 allocations and hence
also work if memory is fragmented.

For reference a call trace where reading from /proc/stat failed:

sadc: page allocation failure: order:4, mode:0x1040d0
CPU: 1 PID: 192063 Comm: sadc Not tainted 3.10.0-123.el7.s390x #1
[...]
Call Trace:
show_stack+0x6c/0xe8
warn_alloc_failed+0xd6/0x138
__alloc_pages_nodemask+0x9da/0xb68
__get_free_pages+0x2e/0x58
kmalloc_order_trace+0x44/0xc0
stat_open+0x5a/0xd8
proc_reg_open+0x8a/0x140
do_dentry_open+0x1bc/0x2c8
finish_open+0x46/0x60
do_last+0x382/0x10d0
path_openat+0xc8/0x4f8
do_filp_open+0x46/0xa8
do_sys_open+0x114/0x1f0
sysc_tracego+0x14/0x1a

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Tested-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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
fs/seq_file.c | 30 +++++++++++++++++++++---------
1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 092951efaf43..6e050e26af43 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -8,8 +8,10 @@
#include <linux/fs.h>
#include <linux/export.h>
#include <linux/seq_file.h>
+#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/cred.h>
+#include <linux/mm.h>

#include <asm/uaccess.h>
#include <asm/page.h>
@@ -30,6 +32,16 @@ static void seq_set_overflow(struct seq_file *m)
m->count = m->size;
}

+static void *seq_buf_alloc(unsigned long size)
+{
+ void *buf;
+
+ buf = kmalloc(size, GFP_KERNEL | __GFP_NOWARN);
+ if (!buf && size > PAGE_SIZE)
+ buf = vmalloc(size);
+ return buf;
+}
+
/**
* seq_open - initialize sequential file
* @file: file we initialize
@@ -96,7 +108,7 @@ static int traverse(struct seq_file *m, loff_t offset)
return 0;
}
if (!m->buf) {
- m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
+ m->buf = seq_buf_alloc(m->size = PAGE_SIZE);
if (!m->buf)
return -ENOMEM;
}
@@ -135,9 +147,9 @@ static int traverse(struct seq_file *m, loff_t offset)

Eoverflow:
m->op->stop(m, p);
- kfree(m->buf);
+ kvfree(m->buf);
m->count = 0;
- m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
+ m->buf = seq_buf_alloc(m->size <<= 1);
return !m->buf ? -ENOMEM : -EAGAIN;
}

@@ -192,7 +204,7 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)

/* grab buffer if we didn't have one */
if (!m->buf) {
- m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
+ m->buf = seq_buf_alloc(m->size = PAGE_SIZE);
if (!m->buf)
goto Enomem;
}
@@ -232,9 +244,9 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
if (m->count < m->size)
goto Fill;
m->op->stop(m, p);
- kfree(m->buf);
+ kvfree(m->buf);
m->count = 0;
- m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
+ m->buf = seq_buf_alloc(m->size <<= 1);
if (!m->buf)
goto Enomem;
m->version = 0;
@@ -350,7 +362,7 @@ EXPORT_SYMBOL(seq_lseek);
int seq_release(struct inode *inode, struct file *file)
{
struct seq_file *m = file->private_data;
- kfree(m->buf);
+ kvfree(m->buf);
kfree(m);
return 0;
}
@@ -605,13 +617,13 @@ EXPORT_SYMBOL(single_open);
int single_open_size(struct file *file, int (*show)(struct seq_file *, void *),
void *data, size_t size)
{
- char *buf = kmalloc(size, GFP_KERNEL);
+ char *buf = seq_buf_alloc(size);
int ret;
if (!buf)
return -ENOMEM;
ret = single_open(file, show, data);
if (ret) {
- kfree(buf);
+ kvfree(buf);
return ret;
}
((struct seq_file *)file->private_data)->buf = buf;
--
2.3.7