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[PATCH 4.4 14/29] zswap: disable changing params if init fails

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

------------------

From: Dan Streetman <ddstreet@ieee.org>

commit d7b028f56a971a2e4d8d7887540a144eeefcd4ab upstream.

Add zswap_init_failed bool that prevents changing any of the module
params, if init_zswap() fails, and set zswap_enabled to false.  Change
'enabled' param to a callback, and check zswap_init_failed before
allowing any change to 'enabled', 'zpool', or 'compressor' params.

Any driver that is built-in to the kernel will not be unloaded if its
init function returns error, and its module params remain accessible for
users to change via sysfs.  Since zswap uses param callbacks, which
assume that zswap has been initialized, changing the zswap params after
a failed initialization will result in WARNING due to the param
callbacks expecting a pool to already exist.  This prevents that by
immediately exiting any of the param callbacks if initialization failed.

This was reported here:
  https://marc.info/?l=linux-mm&m=147004228125528&w=4

And fixes this WARNING:
  [  429.723476] WARNING: CPU: 0 PID: 5140 at mm/zswap.c:503 __zswap_pool_current+0x56/0x60

The warning is just noise, and not serious.  However, when init fails,
zswap frees all its percpu dstmem pages and its kmem cache.  The kmem
cache might be serious, if kmem_cache_alloc(NULL, gfp) has problems; but
the percpu dstmem pages are definitely a problem, as they're used as
temporary buffer for compressed pages before copying into place in the
zpool.

If the user does get zswap enabled after an init failure, then zswap
will likely Oops on the first page it tries to compress (or worse, start
corrupting memory).

Fixes: 90b0fc26d5db ("zswap: change zpool/compressor at runtime")
Link: http://lkml.kernel.org/r/20170124200259.16191-2-ddstreet@ieee.org
Signed-off-by: Dan Streetman <dan.streetman@canonical.com>
Reported-by: Marcin Miroslaw <marcin@mejor.pl>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/zswap.c |   30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -78,7 +78,13 @@ static u64 zswap_duplicate_entry;
 
 /* Enable/disable zswap (disabled by default) */
 static bool zswap_enabled;
-module_param_named(enabled, zswap_enabled, bool, 0644);
+static int zswap_enabled_param_set(const char *,
+				   const struct kernel_param *);
+static struct kernel_param_ops zswap_enabled_param_ops = {
+	.set =		zswap_enabled_param_set,
+	.get =		param_get_bool,
+};
+module_param_cb(enabled, &zswap_enabled_param_ops, &zswap_enabled, 0644);
 
 /* Crypto compressor to use */
 #define ZSWAP_COMPRESSOR_DEFAULT "lzo"
@@ -176,6 +182,9 @@ static atomic_t zswap_pools_count = ATOM
 /* used by param callback function */
 static bool zswap_init_started;
 
+/* fatal error during init */
+static bool zswap_init_failed;
+
 /*********************************
 * helpers and fwd declarations
 **********************************/
@@ -702,6 +711,11 @@ static int __zswap_param_set(const char
 	char *s = strstrip((char *)val);
 	int ret;
 
+	if (zswap_init_failed) {
+		pr_err("can't set param, initialization failed\n");
+		return -ENODEV;
+	}
+
 	/* no change required */
 	if (!strcmp(s, *(char **)kp->arg))
 		return 0;
@@ -781,6 +795,17 @@ static int zswap_zpool_param_set(const c
 	return __zswap_param_set(val, kp, NULL, zswap_compressor);
 }
 
+static int zswap_enabled_param_set(const char *val,
+				   const struct kernel_param *kp)
+{
+	if (zswap_init_failed) {
+		pr_err("can't enable, initialization failed\n");
+		return -ENODEV;
+	}
+
+	return param_set_bool(val, kp);
+}
+
 /*********************************
 * writeback code
 **********************************/
@@ -1267,6 +1292,9 @@ pool_fail:
 dstmem_fail:
 	zswap_entry_cache_destroy();
 cache_fail:
+	/* if built-in, we aren't unloaded on failure; don't allow use */
+	zswap_init_failed = true;
+	zswap_enabled = false;
 	return -ENOMEM;
 }
 /* must be late so crypto has time to come up */

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[PATCH 4.4 00/29] 4.4.48-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 23/29] USB: serial: qcserial: add Dell DW5570 QDL Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 13/29] svcrpc: fix oops in absence of krb5 module Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 07/29] perf/core: Fix PERF_RECORD_MMAP2 prot/flags for anonymous memory Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 29/29] base/memory, hotplug: fix a kernel oops in show_valid_zones() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 20/29] percpu-refcount: fix reference leak during percpu-atomic transition Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 18/29] can: bcm: fix hrtimer/tasklet termination in bcm op removal Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 24/29] USB: serial: pl2303: add ATEN device ID Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 08/29] ata: sata_mv:- Handle return value of devm_ioremap. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 11/29] powerpc: Add missing error check to prom_find_boot_cpu() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 21/29] HID: wacom: Fix poor prox handling in wacom_pl_irq Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 03/29] drm/nouveau/disp/gt215: Fix HDA ELD handling (thus, HDMI audio) on gt215 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 28/29] x86/irq: Make irq activate operations symmetric Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 02/29] ext4: validate s_first_meta_bg at mount time Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 15/29] cifs: initialize file_info_lock Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 26/29] usb: gadget: f_fs: Assorted buffer overflow checks. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 04/29] drm/nouveau/nv1a,nv1f/disp: fix memory clock rate retrieval Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 13:50 +0100
  [PATCH 4.4 01/29] PCI/ASPM: Handle PCI-to-PCIe bridges as roots of PCIe hierarchies Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 14:00 +0100
  [PATCH 4.4 14/29] zswap: disable changing params if init fails Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 14:00 +0100
  [PATCH 4.4 16/29] mm/memory_hotplug.c: check start_pfn in test_pages_in_a_zone() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 14:00 +0100
  [PATCH 4.4 12/29] NFSD: Fix a null reference case in find_or_create_lock_stateid() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 14:00 +0100
  [PATCH 4.4 19/29] mmc: sdhci: Ignore unexpected CARD_INT interrupts Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-07 14:00 +0100
  Re: [PATCH 4.4 00/29] 4.4.48-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-02-07 17:00 +0100
  Re: [PATCH 4.4 00/29] 4.4.48-stable review Guenter Roeck <linux@roeck-us.net> - 2017-02-07 22:50 +0100
  Re: [PATCH 4.4 00/29] 4.4.48-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-08 07:40 +0100
    Re: [PATCH 4.4 00/29] 4.4.48-stable review Kevin Hilman <khilman@baylibre.com> - 2017-02-08 20:50 +0100
      Re: [PATCH 4.4 00/29] 4.4.48-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-08 21:10 +0100

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