[PATCH 18/20] dm: clean up GFP_NIO usage

[Michal Hocko]

From: Michal Hocko <mho...@suse.com>

copy_params uses GFP_NOIO for explicit allocation requests because this
might be called from the suspend path. To quote Mikulas:
: The LVM tool calls suspend and resume ioctls on device mapper block
: devices.
:
: When a device is suspended, any bio sent to the device is held. If the
: resume ioctl did GFP_KERNEL allocation, the allocation could get stuck
: trying to write some dirty cached pages to the suspended device.
:
: The LVM tool and the dmeventd daemon use mlock to lock its address space,
: so the copy_from_user/copy_to_user call cannot trigger a page fault.

Relying on the mlock is quite fragile and we have a better way in kernel
to enfore NOIO which is already used for the vmalloc fallback. Just use
memalloc_noio_{save,restore} around the whole copy_params function which
will force the same also to the page fult paths via copy_{from,to}_user.

While we are there we can also remove __GFP_NOMEMALLOC because copy_params
is never called from MEMALLOC context (e.g. during the reclaim).

Cc: Shaohua Li <s...@kernel.org>
Cc: Mikulas Patocka <mpato...@redhat.com>
Cc: dm-de...@redhat.com
Signed-off-by: Michal Hocko <mho...@suse.com>
---
 drivers/md/dm-ioctl.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 2c7ca258c4e4..fe0b57d7573c 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1715,16 +1715,13 @@ static int copy_params(struct dm_ioctl __user *user, 
struct dm_ioctl *param_kern
         */
        dmi = NULL;
        if (param_kernel->data_size <= KMALLOC_MAX_SIZE) {
-               dmi = kmalloc(param_kernel->data_size, GFP_NOIO | __GFP_NORETRY 
| __GFP_NOMEMALLOC | __GFP_NOWARN);
+               dmi = kmalloc(param_kernel->data_size, GFP_KERNEL | 
__GFP_NORETRY | __GFP_NOWARN);
                if (dmi)
                        *param_flags |= DM_PARAMS_KMALLOC;
        }
 
        if (!dmi) {
-               unsigned noio_flag;
-               noio_flag = memalloc_noio_save();
-               dmi = __vmalloc(param_kernel->data_size, GFP_NOIO | __GFP_HIGH 
| __GFP_HIGHMEM, PAGE_KERNEL);
-               memalloc_noio_restore(noio_flag);
+               dmi = __vmalloc(param_kernel->data_size, GFP_KERNEL | 
__GFP_HIGH | __GFP_HIGHMEM, PAGE_KERNEL);
                if (dmi)
                        *param_flags |= DM_PARAMS_VMALLOC;
        }
@@ -1801,6 +1798,7 @@ static int ctl_ioctl(uint command, struct dm_ioctl __user 
*user)
        ioctl_fn fn = NULL;
        size_t input_param_size;
        struct dm_ioctl param_kernel;
+       unsigned noio_flag;
 
        /* only root can play with this */
        if (!capable(CAP_SYS_ADMIN))
@@ -1832,9 +1830,12 @@ static int ctl_ioctl(uint command, struct dm_ioctl 
__user *user)
        }
 
        /*
-        * Copy the parameters into kernel space.
+        * Copy the parameters into kernel space. Make sure that no IO is 
triggered
+        * from the allocation paths because this might be called during the 
suspend.
         */
+       noio_flag = memalloc_noio_save();
        r = copy_params(user, &param_kernel, ioctl_flags, &param, &param_flags);
+       memalloc_noio_restore(noio_flag);
 
        if (r)
                return r;
-- 
2.8.0.rc3