From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754028AbdHQWMV (ORCPT ); Thu, 17 Aug 2017 18:12:21 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:57752 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753876AbdHQWF5 (ORCPT ); Thu, 17 Aug 2017 18:05:57 -0400 From: Laurent Dufour To: paulmck@linux.vnet.ibm.com, peterz@infradead.org, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org Subject: [PATCH v2 06/20] mm: RCU free VMAs Date: Fri, 18 Aug 2017 00:05:05 +0200 X-Mailer: git-send-email 2.7.4 In-Reply-To: <1503007519-26777-1-git-send-email-ldufour@linux.vnet.ibm.com> References: <1503007519-26777-1-git-send-email-ldufour@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17081722-0008-0000-0000-0000048E7A7E X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17081722-0009-0000-0000-00001E1E7D75 Message-Id: <1503007519-26777-7-git-send-email-ldufour@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-08-17_12:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=2 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1708170357 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra Manage the VMAs with SRCU such that we can do a lockless VMA lookup. We put the fput(vma->vm_file) in the SRCU callback, this keeps files valid during speculative faults, this is possible due to the delayed fput work by Al Viro -- do we need srcu_barrier() in unmount someplace? We guard the mm_rb tree with a seqlock (this could be a seqcount but we'd have to disable preemption around the write side in order to make the retry loop in __read_seqcount_begin() work) such that we can know if the rb tree walk was correct. We cannot trust the restult of a lockless tree walk in the face of concurrent tree rotations; although we can trust on the termination of such walks -- tree rotations guarantee the end result is a tree again after all. Furthermore, we rely on the WMB implied by the write_seqlock/count_begin() to separate the VMA initialization and the publishing stores, analogous to the RELEASE in rcu_assign_pointer(). We also rely on the RMB from read_seqretry() to separate the vma load from further loads like the smp_read_barrier_depends() in regular RCU. We must not touch the vmacache while doing SRCU lookups as that is not properly serialized against changes. We update gap information after publishing the VMA, but A) we don't use that and B) the seqlock read side would fix that anyhow. We clear vma->vm_rb for nodes removed from the vma tree such that we can easily detect such 'dead' nodes, we rely on the WMB from write_sequnlock() to separate the tree removal and clearing the node. Provide find_vma_srcu() which wraps the required magic. Signed-off-by: Peter Zijlstra (Intel) [Remove the warnings in description about the SRCU global lock which has been removed now] [Rename vma_is_dead() to vma_has_changed() and move its adding to the next patch] Signed-off-by: Laurent Dufour --- include/linux/mm_types.h | 2 + kernel/fork.c | 1 + mm/init-mm.c | 1 + mm/internal.h | 5 +++ mm/mmap.c | 100 +++++++++++++++++++++++++++++++++++------------ 5 files changed, 83 insertions(+), 26 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 642aad26b32f..f3851b250fde 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -343,6 +343,7 @@ struct vm_area_struct { #endif struct vm_userfaultfd_ctx vm_userfaultfd_ctx; seqcount_t vm_sequence; + struct rcu_head vm_rcu_head; } __randomize_layout; struct core_thread { @@ -360,6 +361,7 @@ struct kioctx_table; struct mm_struct { struct vm_area_struct *mmap; /* list of VMAs */ struct rb_root mm_rb; + seqlock_t mm_seq; u32 vmacache_seqnum; /* per-thread vmacache */ #ifdef CONFIG_MMU unsigned long (*get_unmapped_area) (struct file *filp, diff --git a/kernel/fork.c b/kernel/fork.c index e075b7780421..f28aa54c668c 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -791,6 +791,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, mm->mmap = NULL; mm->mm_rb = RB_ROOT; mm->vmacache_seqnum = 0; + seqlock_init(&mm->mm_seq); atomic_set(&mm->mm_users, 1); atomic_set(&mm->mm_count, 1); init_rwsem(&mm->mmap_sem); diff --git a/mm/init-mm.c b/mm/init-mm.c index 975e49f00f34..2b1fa061684f 100644 --- a/mm/init-mm.c +++ b/mm/init-mm.c @@ -16,6 +16,7 @@ struct mm_struct init_mm = { .mm_rb = RB_ROOT, + .mm_seq = __SEQLOCK_UNLOCKED(init_mm.mm_seq), .pgd = swapper_pg_dir, .mm_users = ATOMIC_INIT(2), .mm_count = ATOMIC_INIT(1), diff --git a/mm/internal.h b/mm/internal.h index 4ef49fc55e58..736540f15936 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -40,6 +40,11 @@ void page_writeback_init(void); int do_swap_page(struct vm_fault *vmf); +extern struct srcu_struct vma_srcu; + +extern struct vm_area_struct *find_vma_srcu(struct mm_struct *mm, + unsigned long addr); + void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma, unsigned long floor, unsigned long ceiling); diff --git a/mm/mmap.c b/mm/mmap.c index b480043e38fb..34a7f1bdffe4 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -159,6 +159,23 @@ void unlink_file_vma(struct vm_area_struct *vma) } } +DEFINE_SRCU(vma_srcu); + +static void __free_vma(struct rcu_head *head) +{ + struct vm_area_struct *vma = + container_of(head, struct vm_area_struct, vm_rcu_head); + + if (vma->vm_file) + fput(vma->vm_file); + kmem_cache_free(vm_area_cachep, vma); +} + +static void free_vma(struct vm_area_struct *vma) +{ + call_srcu(&vma_srcu, &vma->vm_rcu_head, __free_vma); +} + /* * Close a vm structure and free it, returning the next. */ @@ -169,10 +186,8 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma) might_sleep(); if (vma->vm_ops && vma->vm_ops->close) vma->vm_ops->close(vma); - if (vma->vm_file) - fput(vma->vm_file); mpol_put(vma_policy(vma)); - kmem_cache_free(vm_area_cachep, vma); + free_vma(vma); return next; } @@ -410,26 +425,37 @@ static void vma_gap_update(struct vm_area_struct *vma) } static inline void vma_rb_insert(struct vm_area_struct *vma, - struct rb_root *root) + struct mm_struct *mm) { + struct rb_root *root = &mm->mm_rb; + /* All rb_subtree_gap values must be consistent prior to insertion */ validate_mm_rb(root, NULL); rb_insert_augmented(&vma->vm_rb, root, &vma_gap_callbacks); } -static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root) +static void __vma_rb_erase(struct vm_area_struct *vma, struct mm_struct *mm) { + struct rb_root *root = &mm->mm_rb; /* * Note rb_erase_augmented is a fairly large inline function, * so make sure we instantiate it only once with our desired * augmented rbtree callbacks. */ + write_seqlock(&mm->mm_seq); rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks); + write_sequnlock(&mm->mm_seq); /* wmb */ + + /* + * Ensure the removal is complete before clearing the node. + * Matched by vma_has_changed()/handle_speculative_fault(). + */ + RB_CLEAR_NODE(&vma->vm_rb); } static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma, - struct rb_root *root, + struct mm_struct *mm, struct vm_area_struct *ignore) { /* @@ -437,21 +463,21 @@ static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma, * with the possible exception of the "next" vma being erased if * next->vm_start was reduced. */ - validate_mm_rb(root, ignore); + validate_mm_rb(&mm->mm_rb, ignore); - __vma_rb_erase(vma, root); + __vma_rb_erase(vma, mm); } static __always_inline void vma_rb_erase(struct vm_area_struct *vma, - struct rb_root *root) + struct mm_struct *mm) { /* * All rb_subtree_gap values must be consistent prior to erase, * with the possible exception of the vma being erased. */ - validate_mm_rb(root, vma); + validate_mm_rb(&mm->mm_rb, vma); - __vma_rb_erase(vma, root); + __vma_rb_erase(vma, mm); } /* @@ -568,10 +594,12 @@ void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma, * immediately update the gap to the correct value. Finally we * rebalance the rbtree after all augmented values have been set. */ + write_seqlock(&mm->mm_seq); rb_link_node(&vma->vm_rb, rb_parent, rb_link); vma->rb_subtree_gap = 0; vma_gap_update(vma); - vma_rb_insert(vma, &mm->mm_rb); + vma_rb_insert(vma, mm); + write_sequnlock(&mm->mm_seq); } static void __vma_link_file(struct vm_area_struct *vma) @@ -647,7 +675,7 @@ static __always_inline void __vma_unlink_common(struct mm_struct *mm, { struct vm_area_struct *next; - vma_rb_erase_ignore(vma, &mm->mm_rb, ignore); + vma_rb_erase_ignore(vma, mm, ignore); next = vma->vm_next; if (has_prev) prev->vm_next = next; @@ -901,15 +929,13 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, } if (remove_next) { - if (file) { + if (file) uprobe_munmap(next, next->vm_start, next->vm_end); - fput(file); - } if (next->anon_vma) anon_vma_merge(vma, next); mm->map_count--; mpol_put(vma_policy(next)); - kmem_cache_free(vm_area_cachep, next); + free_vma(next); write_seqcount_end(&next->vm_sequence); /* * In mprotect's case 6 (see comments on vma_merge), @@ -2130,15 +2156,10 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, EXPORT_SYMBOL(get_unmapped_area); /* Look up the first VMA which satisfies addr < vm_end, NULL if none. */ -struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) +static struct vm_area_struct *__find_vma(struct mm_struct *mm, unsigned long addr) { struct rb_node *rb_node; - struct vm_area_struct *vma; - - /* Check the cache first. */ - vma = vmacache_find(mm, addr); - if (likely(vma)) - return vma; + struct vm_area_struct *vma = NULL; rb_node = mm->mm_rb.rb_node; @@ -2156,13 +2177,40 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) rb_node = rb_node->rb_right; } + return vma; +} + +struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) +{ + struct vm_area_struct *vma; + + /* Check the cache first. */ + vma = vmacache_find(mm, addr); + if (likely(vma)) + return vma; + + vma = __find_vma(mm, addr); if (vma) vmacache_update(addr, vma); return vma; } - EXPORT_SYMBOL(find_vma); +struct vm_area_struct *find_vma_srcu(struct mm_struct *mm, unsigned long addr) +{ + struct vm_area_struct *vma; + unsigned int seq; + + WARN_ON_ONCE(!srcu_read_lock_held(&vma_srcu)); + + do { + seq = read_seqbegin(&mm->mm_seq); + vma = __find_vma(mm, addr); + } while (read_seqretry(&mm->mm_seq, seq)); + + return vma; +} + /* * Same as find_vma, but also return a pointer to the previous VMA in *pprev. */ @@ -2530,7 +2578,7 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma, insertion_point = (prev ? &prev->vm_next : &mm->mmap); vma->vm_prev = NULL; do { - vma_rb_erase(vma, &mm->mm_rb); + vma_rb_erase(vma, mm); mm->map_count--; tail_vma = vma; vma = vma->vm_next; -- 2.7.4