kernel/resource: make release_mem_region_adjustable() never fail

Patch series "selective merging of system ram resources", v4.

Some add_memory*() users add memory in small, contiguous memory blocks.
Examples include virtio-mem, hyper-v balloon, and the XEN balloon.

This can quickly result in a lot of memory resources, whereby the actual
resource boundaries are not of interest (e.g., it might be relevant for
DIMMs, exposed via /proc/iomem to user space).  We really want to merge
added resources in this scenario where possible.

Resources are effectively stored in a list-based tree.  Having a lot of
resources not only wastes memory, it also makes traversing that tree more
expensive, and makes /proc/iomem explode in size (e.g., requiring
kexec-tools to manually merge resources when creating a kdump header.  The
current kexec-tools resource count limit does not allow for more than
~100GB of memory with a memory block size of 128MB on x86-64).

Let's allow to selectively merge system ram resources by specifying a new
flag for add_memory*().  Patch #5 contains a /proc/iomem example.  Only
tested with virtio-mem.

This patch (of 8):

Let's make sure splitting a resource on memory hotunplug will never fail.
This will become more relevant once we merge selected System RAM resources
- then, we'll trigger that case more often on memory hotunplug.

In general, this function is already unlikely to fail.  When we remove
memory, we free up quite a lot of metadata (memmap, page tables, memory
block device, etc.).  The only reason it could really fail would be when
injecting allocation errors.

All other error cases inside release_mem_region_adjustable() seem to be
sanity checks if the function would be abused in different context - let's
add WARN_ON_ONCE() in these cases so we can catch them.

[natechancellor@gmail.com: fix use of ternary condition in release_mem_region_adjustable]
Link: https://lkml.kernel.org/r/20200922060748.2452056-1-natechancellor@gmail.com
Link: https://github.com/ClangBuiltLinux/linux/issues/1159
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Anton Blanchard <anton@ozlabs.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Julien Grall <julien@xen.org>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Leonardo Bras <leobras.c@gmail.com>
Cc: Libor Pechacek <lpechacek@suse.cz>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: "Oliver O'Halloran" <oohall@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pingfan Liu <kernelfans@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Roger Pau Monn <roger.pau@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Wei Liu <wei.liu@kernel.org>
Link: https://lkml.kernel.org/r/20200911103459.10306-2-david@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 6c2b06f..52a91f5 100644 (file)
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -248,8 +248,8 @@ extern struct resource * __request_region(struct resource *,
 extern void __release_region(struct resource *, resource_size_t,
                                resource_size_t);
 #ifdef CONFIG_MEMORY_HOTREMOVE
-extern int release_mem_region_adjustable(struct resource *, resource_size_t,
-                               resource_size_t);
+extern void release_mem_region_adjustable(struct resource *, resource_size_t,
+                                         resource_size_t);
 #endif
 
 /* Wrappers for managed devices */

diff --git a/kernel/resource.c b/kernel/resource.c
index f1175ce..4c1c487 100644 (file)
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1258,21 +1258,28 @@ EXPORT_SYMBOL(__release_region);
  *   assumes that all children remain in the lower address entry for
  *   simplicity.  Enhance this logic when necessary.
  */
-int release_mem_region_adjustable(struct resource *parent,
-                                 resource_size_t start, resource_size_t size)
+void release_mem_region_adjustable(struct resource *parent,
+                                  resource_size_t start, resource_size_t size)
 {
+       struct resource *new_res = NULL;
+       bool alloc_nofail = false;
        struct resource **p;
        struct resource *res;
-       struct resource *new_res;
        resource_size_t end;
-       int ret = -EINVAL;
 
        end = start + size - 1;
-       if ((start < parent->start) || (end > parent->end))
-               return ret;
+       if (WARN_ON_ONCE((start < parent->start) || (end > parent->end)))
+               return;
 
-       /* The alloc_resource() result gets checked later */
-       new_res = alloc_resource(GFP_KERNEL);
+       /*
+        * We free up quite a lot of memory on memory hotunplug (esp., memap),
+        * just before releasing the region. This is highly unlikely to
+        * fail - let's play save and make it never fail as the caller cannot
+        * perform any error handling (e.g., trying to re-add memory will fail
+        * similarly).
+        */
+retry:
+       new_res = alloc_resource(GFP_KERNEL | (alloc_nofail ? __GFP_NOFAIL : 0));
 
        p = &parent->child;
        write_lock(&resource_lock);
@@ -1298,7 +1305,6 @@ int release_mem_region_adjustable(struct resource *parent,
                 * so if we are dealing with them, let us just back off here.
                 */
                if (!(res->flags & IORESOURCE_SYSRAM)) {
-                       ret = 0;
                        break;
                }
 
@@ -1315,20 +1321,23 @@ int release_mem_region_adjustable(struct resource *parent,
                        /* free the whole entry */
                        *p = res->sibling;
                        free_resource(res);
-                       ret = 0;
                } else if (res->start == start && res->end != end) {
                        /* adjust the start */
-                       ret = __adjust_resource(res, end + 1,
-                                               res->end - end);
+                       WARN_ON_ONCE(__adjust_resource(res, end + 1,
+                                                      res->end - end));
                } else if (res->start != start && res->end == end) {
                        /* adjust the end */
-                       ret = __adjust_resource(res, res->start,
-                                               start - res->start);
+                       WARN_ON_ONCE(__adjust_resource(res, res->start,
+                                                      start - res->start));
                } else {
-                       /* split into two entries */
+                       /* split into two entries - we need a new resource */
                        if (!new_res) {
-                               ret = -ENOMEM;
-                               break;
+                               new_res = alloc_resource(GFP_ATOMIC);
+                               if (!new_res) {
+                                       alloc_nofail = true;
+                                       write_unlock(&resource_lock);
+                                       goto retry;
+                               }
                        }
                        new_res->name = res->name;
                        new_res->start = end + 1;
@@ -1339,9 +1348,8 @@ int release_mem_region_adjustable(struct resource *parent,
                        new_res->sibling = res->sibling;
                        new_res->child = NULL;
 
-                       ret = __adjust_resource(res, res->start,
-                                               start - res->start);
-                       if (ret)
+                       if (WARN_ON_ONCE(__adjust_resource(res, res->start,
+                                                          start - res->start)))
                                break;
                        res->sibling = new_res;
                        new_res = NULL;
@@ -1352,7 +1360,6 @@ int release_mem_region_adjustable(struct resource *parent,
 
        write_unlock(&resource_lock);
        free_resource(new_res);
-       return ret;
 }
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 1b40eeb..5d9c41e 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1727,26 +1727,6 @@ void try_offline_node(int nid)
 }
 EXPORT_SYMBOL(try_offline_node);
 
-static void __release_memory_resource(resource_size_t start,
-                                     resource_size_t size)
-{
-       int ret;
-
-       /*
-        * When removing memory in the same granularity as it was added,
-        * this function never fails. It might only fail if resources
-        * have to be adjusted or split. We'll ignore the error, as
-        * removing of memory cannot fail.
-        */
-       ret = release_mem_region_adjustable(&iomem_resource, start, size);
-       if (ret) {
-               resource_size_t endres = start + size - 1;
-
-               pr_warn("Unable to release resource <%pa-%pa> (%d)\n",
-                       &start, &endres, ret);
-       }
-}
-
 static int __ref try_remove_memory(int nid, u64 start, u64 size)
 {
        int rc = 0;
@@ -1780,7 +1760,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
                memblock_remove(start, size);
        }
 
-       __release_memory_resource(start, size);
+       release_mem_region_adjustable(&iomem_resource, start, size);
 
        try_offline_node(nid);