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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>
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@ -248,8 +248,8 @@ extern struct resource * __request_region(struct resource *,
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extern void __release_region(struct resource *, resource_size_t,
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resource_size_t);
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#ifdef CONFIG_MEMORY_HOTREMOVE
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extern int release_mem_region_adjustable(struct resource *, resource_size_t,
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resource_size_t);
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extern void release_mem_region_adjustable(struct resource *, resource_size_t,
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resource_size_t);
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#endif
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/* Wrappers for managed devices */
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@ -1258,21 +1258,28 @@ EXPORT_SYMBOL(__release_region);
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* assumes that all children remain in the lower address entry for
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* simplicity. Enhance this logic when necessary.
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*/
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int release_mem_region_adjustable(struct resource *parent,
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resource_size_t start, resource_size_t size)
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void release_mem_region_adjustable(struct resource *parent,
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resource_size_t start, resource_size_t size)
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{
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struct resource *new_res = NULL;
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bool alloc_nofail = false;
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struct resource **p;
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struct resource *res;
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struct resource *new_res;
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resource_size_t end;
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int ret = -EINVAL;
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end = start + size - 1;
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if ((start < parent->start) || (end > parent->end))
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return ret;
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if (WARN_ON_ONCE((start < parent->start) || (end > parent->end)))
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return;
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/* The alloc_resource() result gets checked later */
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new_res = alloc_resource(GFP_KERNEL);
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/*
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* We free up quite a lot of memory on memory hotunplug (esp., memap),
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* just before releasing the region. This is highly unlikely to
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* fail - let's play save and make it never fail as the caller cannot
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* perform any error handling (e.g., trying to re-add memory will fail
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* similarly).
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*/
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retry:
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new_res = alloc_resource(GFP_KERNEL | (alloc_nofail ? __GFP_NOFAIL : 0));
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p = &parent->child;
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write_lock(&resource_lock);
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@ -1298,7 +1305,6 @@ int release_mem_region_adjustable(struct resource *parent,
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* so if we are dealing with them, let us just back off here.
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*/
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if (!(res->flags & IORESOURCE_SYSRAM)) {
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ret = 0;
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break;
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}
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@ -1315,20 +1321,23 @@ int release_mem_region_adjustable(struct resource *parent,
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/* free the whole entry */
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*p = res->sibling;
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free_resource(res);
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ret = 0;
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} else if (res->start == start && res->end != end) {
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/* adjust the start */
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ret = __adjust_resource(res, end + 1,
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res->end - end);
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WARN_ON_ONCE(__adjust_resource(res, end + 1,
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res->end - end));
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} else if (res->start != start && res->end == end) {
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/* adjust the end */
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ret = __adjust_resource(res, res->start,
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start - res->start);
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WARN_ON_ONCE(__adjust_resource(res, res->start,
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start - res->start));
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} else {
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/* split into two entries */
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/* split into two entries - we need a new resource */
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if (!new_res) {
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ret = -ENOMEM;
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break;
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new_res = alloc_resource(GFP_ATOMIC);
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if (!new_res) {
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alloc_nofail = true;
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write_unlock(&resource_lock);
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goto retry;
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}
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}
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new_res->name = res->name;
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new_res->start = end + 1;
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@ -1339,9 +1348,8 @@ int release_mem_region_adjustable(struct resource *parent,
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new_res->sibling = res->sibling;
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new_res->child = NULL;
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ret = __adjust_resource(res, res->start,
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start - res->start);
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if (ret)
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if (WARN_ON_ONCE(__adjust_resource(res, res->start,
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start - res->start)))
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break;
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res->sibling = new_res;
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new_res = NULL;
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@ -1352,7 +1360,6 @@ int release_mem_region_adjustable(struct resource *parent,
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write_unlock(&resource_lock);
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free_resource(new_res);
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return ret;
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}
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#endif /* CONFIG_MEMORY_HOTREMOVE */
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@ -1727,26 +1727,6 @@ void try_offline_node(int nid)
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}
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EXPORT_SYMBOL(try_offline_node);
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static void __release_memory_resource(resource_size_t start,
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resource_size_t size)
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{
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int ret;
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/*
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* When removing memory in the same granularity as it was added,
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* this function never fails. It might only fail if resources
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* have to be adjusted or split. We'll ignore the error, as
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* removing of memory cannot fail.
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*/
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ret = release_mem_region_adjustable(&iomem_resource, start, size);
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if (ret) {
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resource_size_t endres = start + size - 1;
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pr_warn("Unable to release resource <%pa-%pa> (%d)\n",
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&start, &endres, ret);
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}
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}
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static int __ref try_remove_memory(int nid, u64 start, u64 size)
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{
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int rc = 0;
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@ -1780,7 +1760,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
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memblock_remove(start, size);
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}
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__release_memory_resource(start, size);
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release_mem_region_adjustable(&iomem_resource, start, size);
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try_offline_node(nid);
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