![Michal Hocko](/assets/img/avatar_default.png)
There are several blockable mmu notifiers which might sleep in mmu_notifier_invalidate_range_start and that is a problem for the oom_reaper because it needs to guarantee a forward progress so it cannot depend on any sleepable locks. Currently we simply back off and mark an oom victim with blockable mmu notifiers as done after a short sleep. That can result in selecting a new oom victim prematurely because the previous one still hasn't torn its memory down yet. We can do much better though. Even if mmu notifiers use sleepable locks there is no reason to automatically assume those locks are held. Moreover majority of notifiers only care about a portion of the address space and there is absolutely zero reason to fail when we are unmapping an unrelated range. Many notifiers do really block and wait for HW which is harder to handle and we have to bail out though. This patch handles the low hanging fruit. __mmu_notifier_invalidate_range_start gets a blockable flag and callbacks are not allowed to sleep if the flag is set to false. This is achieved by using trylock instead of the sleepable lock for most callbacks and continue as long as we do not block down the call chain. I think we can improve that even further because there is a common pattern to do a range lookup first and then do something about that. The first part can be done without a sleeping lock in most cases AFAICS. The oom_reaper end then simply retries if there is at least one notifier which couldn't make any progress in !blockable mode. A retry loop is already implemented to wait for the mmap_sem and this is basically the same thing. The simplest way for driver developers to test this code path is to wrap userspace code which uses these notifiers into a memcg and set the hard limit to hit the oom. This can be done e.g. after the test faults in all the mmu notifier managed memory and set the hard limit to something really small. Then we are looking for a proper process tear down. [akpm@linux-foundation.org: coding style fixes] [akpm@linux-foundation.org: minor code simplification] Link: http://lkml.kernel.org/r/20180716115058.5559-1-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Acked-by: Christian König <christian.koenig@amd.com> # AMD notifiers Acked-by: Leon Romanovsky <leonro@mellanox.com> # mlx and umem_odp Reported-by: David Rientjes <rientjes@google.com> Cc: "David (ChunMing) Zhou" <David1.Zhou@amd.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Alex Deucher <alexander.deucher@amd.com> Cc: David Airlie <airlied@linux.ie> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Doug Ledford <dledford@redhat.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Mike Marciniszyn <mike.marciniszyn@intel.com> Cc: Dennis Dalessandro <dennis.dalessandro@intel.com> Cc: Sudeep Dutt <sudeep.dutt@intel.com> Cc: Ashutosh Dixit <ashutosh.dixit@intel.com> Cc: Dimitri Sivanich <sivanich@sgi.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Juergen Gross <jgross@suse.com> Cc: "Jérôme Glisse" <jglisse@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Felix Kuehling <felix.kuehling@amd.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
176 lines
5.4 KiB
C
176 lines
5.4 KiB
C
/*
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* Copyright (c) 2014 Mellanox Technologies. All rights reserved.
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*
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* This software is available to you under a choice of one of two
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* licenses. You may choose to be licensed under the terms of the GNU
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* General Public License (GPL) Version 2, available from the file
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* COPYING in the main directory of this source tree, or the
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* OpenIB.org BSD license below:
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*
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* Redistribution and use in source and binary forms, with or
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* without modification, are permitted provided that the following
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* conditions are met:
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*
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* - Redistributions of source code must retain the above
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* copyright notice, this list of conditions and the following
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* disclaimer.
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*
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* - Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following
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* disclaimer in the documentation and/or other materials
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* provided with the distribution.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#ifndef IB_UMEM_ODP_H
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#define IB_UMEM_ODP_H
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#include <rdma/ib_umem.h>
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#include <rdma/ib_verbs.h>
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#include <linux/interval_tree.h>
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struct umem_odp_node {
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u64 __subtree_last;
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struct rb_node rb;
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};
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struct ib_umem_odp {
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/*
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* An array of the pages included in the on-demand paging umem.
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* Indices of pages that are currently not mapped into the device will
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* contain NULL.
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*/
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struct page **page_list;
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/*
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* An array of the same size as page_list, with DMA addresses mapped
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* for pages the pages in page_list. The lower two bits designate
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* access permissions. See ODP_READ_ALLOWED_BIT and
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* ODP_WRITE_ALLOWED_BIT.
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*/
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dma_addr_t *dma_list;
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/*
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* The umem_mutex protects the page_list and dma_list fields of an ODP
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* umem, allowing only a single thread to map/unmap pages. The mutex
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* also protects access to the mmu notifier counters.
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*/
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struct mutex umem_mutex;
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void *private; /* for the HW driver to use. */
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/* When false, use the notifier counter in the ucontext struct. */
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bool mn_counters_active;
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int notifiers_seq;
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int notifiers_count;
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/* A linked list of umems that don't have private mmu notifier
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* counters yet. */
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struct list_head no_private_counters;
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struct ib_umem *umem;
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/* Tree tracking */
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struct umem_odp_node interval_tree;
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struct completion notifier_completion;
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int dying;
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struct work_struct work;
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};
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#ifdef CONFIG_INFINIBAND_ON_DEMAND_PAGING
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int ib_umem_odp_get(struct ib_ucontext *context, struct ib_umem *umem,
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int access);
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struct ib_umem *ib_alloc_odp_umem(struct ib_ucontext *context,
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unsigned long addr,
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size_t size);
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void ib_umem_odp_release(struct ib_umem *umem);
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/*
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* The lower 2 bits of the DMA address signal the R/W permissions for
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* the entry. To upgrade the permissions, provide the appropriate
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* bitmask to the map_dma_pages function.
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*
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* Be aware that upgrading a mapped address might result in change of
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* the DMA address for the page.
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*/
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#define ODP_READ_ALLOWED_BIT (1<<0ULL)
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#define ODP_WRITE_ALLOWED_BIT (1<<1ULL)
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#define ODP_DMA_ADDR_MASK (~(ODP_READ_ALLOWED_BIT | ODP_WRITE_ALLOWED_BIT))
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int ib_umem_odp_map_dma_pages(struct ib_umem *umem, u64 start_offset, u64 bcnt,
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u64 access_mask, unsigned long current_seq);
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void ib_umem_odp_unmap_dma_pages(struct ib_umem *umem, u64 start_offset,
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u64 bound);
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typedef int (*umem_call_back)(struct ib_umem *item, u64 start, u64 end,
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void *cookie);
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/*
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* Call the callback on each ib_umem in the range. Returns the logical or of
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* the return values of the functions called.
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*/
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int rbt_ib_umem_for_each_in_range(struct rb_root_cached *root,
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u64 start, u64 end,
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umem_call_back cb,
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bool blockable, void *cookie);
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/*
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* Find first region intersecting with address range.
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* Return NULL if not found
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*/
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struct ib_umem_odp *rbt_ib_umem_lookup(struct rb_root_cached *root,
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u64 addr, u64 length);
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static inline int ib_umem_mmu_notifier_retry(struct ib_umem *item,
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unsigned long mmu_seq)
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{
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/*
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* This code is strongly based on the KVM code from
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* mmu_notifier_retry. Should be called with
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* the relevant locks taken (item->odp_data->umem_mutex
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* and the ucontext umem_mutex semaphore locked for read).
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*/
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/* Do not allow page faults while the new ib_umem hasn't seen a state
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* with zero notifiers yet, and doesn't have its own valid set of
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* private counters. */
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if (!item->odp_data->mn_counters_active)
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return 1;
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if (unlikely(item->odp_data->notifiers_count))
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return 1;
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if (item->odp_data->notifiers_seq != mmu_seq)
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return 1;
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return 0;
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}
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#else /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
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static inline int ib_umem_odp_get(struct ib_ucontext *context,
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struct ib_umem *umem,
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int access)
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{
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return -EINVAL;
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}
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static inline struct ib_umem *ib_alloc_odp_umem(struct ib_ucontext *context,
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unsigned long addr,
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size_t size)
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{
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return ERR_PTR(-EINVAL);
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}
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static inline void ib_umem_odp_release(struct ib_umem *umem) {}
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#endif /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
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#endif /* IB_UMEM_ODP_H */
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