/*
 * linux/fs/nfs/cache_lib.c
 *
 * Helper routines for the NFS client caches
 *
 * Copyright (c) 2009 Trond Myklebust <Trond.Myklebust@netapp.com>
 */
#include <linux/kmod.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/slab.h>
#include <linux/sunrpc/cache.h>
#include <linux/sunrpc/rpc_pipe_fs.h>
#include <net/net_namespace.h>

#include "cache_lib.h"

#define NFS_CACHE_UPCALL_PATHLEN 256
#define NFS_CACHE_UPCALL_TIMEOUT 15

static char nfs_cache_getent_prog[NFS_CACHE_UPCALL_PATHLEN] =
				"/sbin/nfs_cache_getent";
static unsigned long nfs_cache_getent_timeout = NFS_CACHE_UPCALL_TIMEOUT;

module_param_string(cache_getent, nfs_cache_getent_prog,
		sizeof(nfs_cache_getent_prog), 0600);
MODULE_PARM_DESC(cache_getent, "Path to the client cache upcall program");
module_param_named(cache_getent_timeout, nfs_cache_getent_timeout, ulong, 0600);
MODULE_PARM_DESC(cache_getent_timeout, "Timeout (in seconds) after which "
		"the cache upcall is assumed to have failed");

int nfs_cache_upcall(struct cache_detail *cd, char *entry_name)
{
	static char *envp[] = { "HOME=/",
		"TERM=linux",
		"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
		NULL
	};
	char *argv[] = {
		nfs_cache_getent_prog,
		cd->name,
		entry_name,
		NULL
	};
	int ret = -EACCES;

	if (nfs_cache_getent_prog[0] == '\0')
		goto out;
	ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
	/*
	 * Disable the upcall mechanism if we're getting an ENOENT or
	 * EACCES error. The admin can re-enable it on the fly by using
	 * sysfs to set the 'cache_getent' parameter once the problem
	 * has been fixed.
	 */
	if (ret == -ENOENT || ret == -EACCES)
		nfs_cache_getent_prog[0] = '\0';
out:
	return ret > 0 ? 0 : ret;
}

/*
 * Deferred request handling
 */
void nfs_cache_defer_req_put(struct nfs_cache_defer_req *dreq)
{
	if (atomic_dec_and_test(&dreq->count))
		kfree(dreq);
}

static void nfs_dns_cache_revisit(struct cache_deferred_req *d, int toomany)
{
	struct nfs_cache_defer_req *dreq;

	dreq = container_of(d, struct nfs_cache_defer_req, deferred_req);

	complete(&dreq->completion);
	nfs_cache_defer_req_put(dreq);
}

static struct cache_deferred_req *nfs_dns_cache_defer(struct cache_req *req)
{
	struct nfs_cache_defer_req *dreq;

	dreq = container_of(req, struct nfs_cache_defer_req, req);
	dreq->deferred_req.revisit = nfs_dns_cache_revisit;
	atomic_inc(&dreq->count);

	return &dreq->deferred_req;
}

struct nfs_cache_defer_req *nfs_cache_defer_req_alloc(void)
{
	struct nfs_cache_defer_req *dreq;

	dreq = kzalloc(sizeof(*dreq), GFP_KERNEL);
	if (dreq) {
		init_completion(&dreq->completion);
		atomic_set(&dreq->count, 1);
		dreq->req.defer = nfs_dns_cache_defer;
	}
	return dreq;
}

int nfs_cache_wait_for_upcall(struct nfs_cache_defer_req *dreq)
{
	if (wait_for_completion_timeout(&dreq->completion,
			nfs_cache_getent_timeout * HZ) == 0)
		return -ETIMEDOUT;
	return 0;
}

int nfs_cache_register_sb(struct super_block *sb, struct cache_detail *cd)
{
	int ret;
	struct dentry *dir;

	dir = rpc_d_lookup_sb(sb, "cache");
	ret = sunrpc_cache_register_pipefs(dir, cd->name, 0600, cd);
	dput(dir);
	return ret;
}

int nfs_cache_register_net(struct net *net, struct cache_detail *cd)
{
	struct super_block *pipefs_sb;
	int ret = 0;

	sunrpc_init_cache_detail(cd);
	pipefs_sb = rpc_get_sb_net(net);
	if (pipefs_sb) {
		ret = nfs_cache_register_sb(pipefs_sb, cd);
		rpc_put_sb_net(net);
		if (ret)
			sunrpc_destroy_cache_detail(cd);
	}
	return ret;
}

void nfs_cache_unregister_sb(struct super_block *sb, struct cache_detail *cd)
{
	if (cd->u.pipefs.dir)
		sunrpc_cache_unregister_pipefs(cd);
}

void nfs_cache_unregister_net(struct net *net, struct cache_detail *cd)
{
	struct super_block *pipefs_sb;

	pipefs_sb = rpc_get_sb_net(net);
	if (pipefs_sb) {
		nfs_cache_unregister_sb(pipefs_sb, cd);
		rpc_put_sb_net(net);
	}
	sunrpc_destroy_cache_detail(cd);
}
n value='40'>40</option></select></td></tr><tr><td class='label'>space:</td><td class='ctrl'><select name='ignorews' onchange='this.form.submit();'><option value='0' selected='selected'>include</option><option value='1'>ignore</option></select></td></tr><tr><td class='label'>mode:</td><td class='ctrl'><select name='dt' onchange='this.form.submit();'><option value='0' selected='selected'>unified</option><option value='1'>ssdiff</option><option value='2'>stat only</option></select></td></tr><tr><td/><td class='ctrl'><noscript><input type='submit' value='reload'/></noscript></td></tr></table></form></div><table summary='commit info' class='commit-info'>
<tr><th>author</th><td>Douglas Miller &lt;dougmill@linux.vnet.ibm.com&gt;</td><td class='right'>2017-01-28 06:42:20 -0600</td></tr>
<tr><th>committer</th><td>Tejun Heo &lt;tj@kernel.org&gt;</td><td class='right'>2017-01-28 07:49:42 -0500</td></tr>
<tr><th>commit</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/include/crypto/b128ops.h?id=966d2b04e070bc040319aaebfec09e0144dc3341'>966d2b04e070bc040319aaebfec09e0144dc3341</a> (<a href='/cgit.cgi/linux/net-next.git/patch/include/crypto/b128ops.h?id=966d2b04e070bc040319aaebfec09e0144dc3341'>patch</a>)</td></tr>
<tr><th>tree</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/tree/?id=966d2b04e070bc040319aaebfec09e0144dc3341'>4b96156e3d1dd4dfd6039b7c219c9dc4616da52d</a> /<a href='/cgit.cgi/linux/net-next.git/tree/include/crypto/b128ops.h?id=966d2b04e070bc040319aaebfec09e0144dc3341'>include/crypto/b128ops.h</a></td></tr>
<tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/include/crypto/b128ops.h?id=1b1bc42c1692e9b62756323c675a44cb1a1f9dbd'>1b1bc42c1692e9b62756323c675a44cb1a1f9dbd</a> (<a href='/cgit.cgi/linux/net-next.git/diff/include/crypto/b128ops.h?id=966d2b04e070bc040319aaebfec09e0144dc3341&amp;id2=1b1bc42c1692e9b62756323c675a44cb1a1f9dbd'>diff</a>)</td></tr></table>
<div class='commit-subject'>percpu-refcount: fix reference leak during percpu-atomic transition</div><div class='commit-msg'>percpu_ref_tryget() and percpu_ref_tryget_live() should return
"true" IFF they acquire a reference. But the return value from
atomic_long_inc_not_zero() is a long and may have high bits set,
e.g. PERCPU_COUNT_BIAS, and the return value of the tryget routines
is bool so the reference may actually be acquired but the routines
return "false" which results in a reference leak since the caller
assumes it does not need to do a corresponding percpu_ref_put().

This was seen when performing CPU hotplug during I/O, as hangs in
blk_mq_freeze_queue_wait where percpu_ref_kill (blk_mq_freeze_queue_start)
raced with percpu_ref_tryget (blk_mq_timeout_work).
Sample stack trace:

__switch_to+0x2c0/0x450
__schedule+0x2f8/0x970
schedule+0x48/0xc0
blk_mq_freeze_queue_wait+0x94/0x120
blk_mq_queue_reinit_work+0xb8/0x180
blk_mq_queue_reinit_prepare+0x84/0xa0
cpuhp_invoke_callback+0x17c/0x600
cpuhp_up_callbacks+0x58/0x150
_cpu_up+0xf0/0x1c0
do_cpu_up+0x120/0x150
cpu_subsys_online+0x64/0xe0
device_online+0xb4/0x120
online_store+0xb4/0xc0
dev_attr_store+0x68/0xa0
sysfs_kf_write+0x80/0xb0
kernfs_fop_write+0x17c/0x250
__vfs_write+0x6c/0x1e0
vfs_write+0xd0/0x270
SyS_write+0x6c/0x110
system_call+0x38/0xe0

Examination of the queue showed a single reference (no PERCPU_COUNT_BIAS,
and __PERCPU_REF_DEAD, __PERCPU_REF_ATOMIC set) and no requests.
However, conditions at the time of the race are count of PERCPU_COUNT_BIAS + 0
and __PERCPU_REF_DEAD and __PERCPU_REF_ATOMIC set.

The fix is to make the tryget routines use an actual boolean internally instead
of the atomic long result truncated to a int.

Fixes: e625305b3907 percpu-refcount: make percpu_ref based on longs instead of ints
Link: https://bugzilla.kernel.org/show_bug.cgi?id=190751
Signed-off-by: Douglas Miller &lt;dougmill@linux.vnet.ibm.com&gt;
Reviewed-by: Jens Axboe &lt;axboe@fb.com&gt;
Signed-off-by: Tejun Heo &lt;tj@kernel.org&gt;
Fixes: e625305b3907 ("percpu-refcount: make percpu_ref based on longs instead of ints")
Cc: stable@vger.kernel.org # v3.18+
</div><div class='diffstat-header'><a href='/cgit.cgi/linux/net-next.git/diff/?id=966d2b04e070bc040319aaebfec09e0144dc3341'>Diffstat</a> (limited to 'include/crypto/b128ops.h')</div><table summary='diffstat' class='diffstat'>