June 2021 - Linux-stable-mirror

[patch 19/24] mm,hwpoison: return -EHWPOISON to denote that the page has already been poisoned

by Andrew Morton

From: Aili Yao <yaoaili(a)kingsoft.com> Subject: mm,hwpoison: return -EHWPOISON to denote that the page has already been poisoned When memory_failure() is called with MF_ACTION_REQUIRED on the page that has already been hwpoisoned, memory_failure() could fail to send SIGBUS to the affected process, which results in infinite loop of MCEs. Currently memory_failure() returns 0 if it's called for already hwpoisoned page, then the caller, kill_me_maybe(), could return without sending SIGBUS to current process. An action required MCE is raised when the current process accesses to the broken memory, so no SIGBUS means that the current process continues to run and access to the error page again soon, so running into MCE loop. This issue can arise for example in the following scenarios: - Two or more threads access to the poisoned page concurrently. If local MCE is enabled, MCE handler independently handles the MCE events. So there's a race among MCE events, and the second or latter threads fall into the situation in question. - If there was a precedent memory error event and memory_failure() for the event failed to unmap the error page for some reason, the subsequent memory access to the error page triggers the MCE loop situation. To fix the issue, make memory_failure() return an error code when the error page has already been hwpoisoned. This allows memory error handler to control how it sends signals to userspace. And make sure that any process touching a hwpoisoned page should get a SIGBUS even in "already hwpoisoned" path of memory_failure() as is done in page fault path. Link: https://lkml.kernel.org/r/20210521030156.2612074-3-nao.horiguchi@gmail.com Signed-off-by: Aili Yao <yaoaili(a)kingsoft.com> Signed-off-by: Naoya Horiguchi <naoya.horiguchi(a)nec.com> Reviewed-by: Oscar Salvador <osalvador(a)suse.de> Cc: Andy Lutomirski <luto(a)kernel.org> Cc: Borislav Petkov <bp(a)alien8.de> Cc: Borislav Petkov <bp(a)suse.de> Cc: David Hildenbrand <david(a)redhat.com> Cc: Jue Wang <juew(a)google.com> Cc: Tony Luck <tony.luck(a)intel.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/memory-failure.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/mm/memory-failure.c~mmhwpoison-return-ehwpoison-to-denote-that-the-page-has-already-been-poisoned +++ a/mm/memory-failure.c @@ -1253,7 +1253,7 @@ static int memory_failure_hugetlb(unsign if (TestSetPageHWPoison(head)) { pr_err("Memory failure: %#lx: already hardware poisoned\n", pfn); - return 0; + return -EHWPOISON; } num_poisoned_pages_inc(); @@ -1461,6 +1461,7 @@ try_again: if (TestSetPageHWPoison(p)) { pr_err("Memory failure: %#lx: already hardware poisoned\n", pfn); + res = -EHWPOISON; goto unlock_mutex; } _

3 years, 3 months

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[patch 18/24] mm/memory-failure: use a mutex to avoid memory_failure() races

by Andrew Morton

From: Tony Luck <tony.luck(a)intel.com> Subject: mm/memory-failure: use a mutex to avoid memory_failure() races Patch series "mm,hwpoison: fix sending SIGBUS for Action Required MCE", v5. I wrote this patchset to materialize what I think is the current allowable solution mentioned by the previous discussion [1]. I simply borrowed Tony's mutex patch and Aili's return code patch, then I queued another one to find error virtual address in the best effort manner. I know that this is not a perfect solution, but should work for some typical case. [1]: https://lore.kernel.org/linux-mm/20210331192540.2141052f@alex-virtual-machi… This patch (of 2): There can be races when multiple CPUs consume poison from the same page. The first into memory_failure() atomically sets the HWPoison page flag and begins hunting for tasks that map this page. Eventually it invalidates those mappings and may send a SIGBUS to the affected tasks. But while all that work is going on, other CPUs see a "success" return code from memory_failure() and so they believe the error has been handled and continue executing. Fix by wrapping most of the internal parts of memory_failure() in a mutex. [akpm(a)linux-foundation.org: make mf_mutex local to memory_failure()] Link: https://lkml.kernel.org/r/20210521030156.2612074-1-nao.horiguchi@gmail.com Link: https://lkml.kernel.org/r/20210521030156.2612074-2-nao.horiguchi@gmail.com Signed-off-by: Tony Luck <tony.luck(a)intel.com> Signed-off-by: Naoya Horiguchi <naoya.horiguchi(a)nec.com> Reviewed-by: Borislav Petkov <bp(a)suse.de> Reviewed-by: Oscar Salvador <osalvador(a)suse.de> Cc: Aili Yao <yaoaili(a)kingsoft.com> Cc: Andy Lutomirski <luto(a)kernel.org> Cc: Borislav Petkov <bp(a)alien8.de> Cc: David Hildenbrand <david(a)redhat.com> Cc: Jue Wang <juew(a)google.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/memory-failure.c | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-) --- a/mm/memory-failure.c~mm-memory-failure-use-a-mutex-to-avoid-memory_failure-races +++ a/mm/memory-failure.c @@ -1429,9 +1429,10 @@ int memory_failure(unsigned long pfn, in struct page *hpage; struct page *orig_head; struct dev_pagemap *pgmap; - int res; + int res = 0; unsigned long page_flags; bool retry = true; + static DEFINE_MUTEX(mf_mutex); if (!sysctl_memory_failure_recovery) panic("Memory failure on page %lx", pfn); @@ -1449,13 +1450,18 @@ int memory_failure(unsigned long pfn, in return -ENXIO; } + mutex_lock(&mf_mutex); + try_again: - if (PageHuge(p)) - return memory_failure_hugetlb(pfn, flags); + if (PageHuge(p)) { + res = memory_failure_hugetlb(pfn, flags); + goto unlock_mutex; + } + if (TestSetPageHWPoison(p)) { pr_err("Memory failure: %#lx: already hardware poisoned\n", pfn); - return 0; + goto unlock_mutex; } orig_head = hpage = compound_head(p); @@ -1488,17 +1494,19 @@ try_again: res = MF_FAILED; } action_result(pfn, MF_MSG_BUDDY, res); - return res == MF_RECOVERED ? 0 : -EBUSY; + res = res == MF_RECOVERED ? 0 : -EBUSY; } else { action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED); - return -EBUSY; + res = -EBUSY; } + goto unlock_mutex; } if (PageTransHuge(hpage)) { if (try_to_split_thp_page(p, "Memory Failure") < 0) { action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED); - return -EBUSY; + res = -EBUSY; + goto unlock_mutex; } VM_BUG_ON_PAGE(!page_count(p), p); } @@ -1522,7 +1530,7 @@ try_again: if (PageCompound(p) && compound_head(p) != orig_head) { action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED); res = -EBUSY; - goto out; + goto unlock_page; } /* @@ -1542,14 +1550,14 @@ try_again: num_poisoned_pages_dec(); unlock_page(p); put_page(p); - return 0; + goto unlock_mutex; } if (hwpoison_filter(p)) { if (TestClearPageHWPoison(p)) num_poisoned_pages_dec(); unlock_page(p); put_page(p); - return 0; + goto unlock_mutex; } /* @@ -1573,7 +1581,7 @@ try_again: if (!hwpoison_user_mappings(p, pfn, flags, &p)) { action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED); res = -EBUSY; - goto out; + goto unlock_page; } /* @@ -1582,13 +1590,15 @@ try_again: if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) { action_result(pfn, MF_MSG_TRUNCATED_LRU, MF_IGNORED); res = -EBUSY; - goto out; + goto unlock_page; } identify_page_state: res = identify_page_state(pfn, p, page_flags); -out: +unlock_page: unlock_page(p); +unlock_mutex: + mutex_unlock(&mf_mutex); return res; } EXPORT_SYMBOL_GPL(memory_failure); _

3 years, 3 months

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[patch 17/24] mm, futex: fix shared futex pgoff on shmem huge page

by Andrew Morton

From: Hugh Dickins <hughd(a)google.com> Subject: mm, futex: fix shared futex pgoff on shmem huge page If more than one futex is placed on a shmem huge page, it can happen that waking the second wakes the first instead, and leaves the second waiting: the key's shared.pgoff is wrong. When 3.11 commit 13d60f4b6ab5 ("futex: Take hugepages into account when generating futex_key"), the only shared huge pages came from hugetlbfs, and the code added to deal with its exceptional page->index was put into hugetlb source. Then that was missed when 4.8 added shmem huge pages. page_to_pgoff() is what others use for this nowadays: except that, as currently written, it gives the right answer on hugetlbfs head, but nonsense on hugetlbfs tails. Fix that by calling hugetlbfs-specific hugetlb_basepage_index() on PageHuge tails as well as on head. Yes, it's unconventional to declare hugetlb_basepage_index() there in pagemap.h, rather than in hugetlb.h; but I do not expect anything but page_to_pgoff() ever to need it. [akpm(a)linux-foundation.org: give hugetlb_basepage_index() prototype the correct scope] Link: https://lkml.kernel.org/r/b17d946b-d09-326e-b42a-52884c36df32@google.com Fixes: 800d8c63b2e9 ("shmem: add huge pages support") Reported-by: Neel Natu <neelnatu(a)google.com> Signed-off-by: Hugh Dickins <hughd(a)google.com> Reviewed-by: Matthew Wilcox (Oracle) <willy(a)infradead.org> Acked-by: Thomas Gleixner <tglx(a)linutronix.de> Cc: "Kirill A. Shutemov" <kirill.shutemov(a)linux.intel.com> Cc: Zhang Yi <wetpzy(a)gmail.com> Cc: Mel Gorman <mgorman(a)techsingularity.net> Cc: Mike Kravetz <mike.kravetz(a)oracle.com> Cc: Ingo Molnar <mingo(a)redhat.com> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Darren Hart <dvhart(a)infradead.org> Cc: Davidlohr Bueso <dave(a)stgolabs.net> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- include/linux/hugetlb.h | 16 ---------------- include/linux/pagemap.h | 13 +++++++------ kernel/futex.c | 3 +-- mm/hugetlb.c | 5 +---- 4 files changed, 9 insertions(+), 28 deletions(-) --- a/include/linux/hugetlb.h~mm-futex-fix-shared-futex-pgoff-on-shmem-huge-page +++ a/include/linux/hugetlb.h @@ -741,17 +741,6 @@ static inline int hstate_index(struct hs return h - hstates; } -pgoff_t __basepage_index(struct page *page); - -/* Return page->index in PAGE_SIZE units */ -static inline pgoff_t basepage_index(struct page *page) -{ - if (!PageCompound(page)) - return page->index; - - return __basepage_index(page); -} - extern int dissolve_free_huge_page(struct page *page); extern int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn); @@ -988,11 +977,6 @@ static inline int hstate_index(struct hs return 0; } -static inline pgoff_t basepage_index(struct page *page) -{ - return page->index; -} - static inline int dissolve_free_huge_page(struct page *page) { return 0; --- a/include/linux/pagemap.h~mm-futex-fix-shared-futex-pgoff-on-shmem-huge-page +++ a/include/linux/pagemap.h @@ -516,7 +516,7 @@ static inline struct page *read_mapping_ } /* - * Get index of the page with in radix-tree + * Get index of the page within radix-tree (but not for hugetlb pages). * (TODO: remove once hugetlb pages will have ->index in PAGE_SIZE) */ static inline pgoff_t page_to_index(struct page *page) @@ -535,15 +535,16 @@ static inline pgoff_t page_to_index(stru return pgoff; } +extern pgoff_t hugetlb_basepage_index(struct page *page); + /* - * Get the offset in PAGE_SIZE. - * (TODO: hugepage should have ->index in PAGE_SIZE) + * Get the offset in PAGE_SIZE (even for hugetlb pages). + * (TODO: hugetlb pages should have ->index in PAGE_SIZE) */ static inline pgoff_t page_to_pgoff(struct page *page) { - if (unlikely(PageHeadHuge(page))) - return page->index << compound_order(page); - + if (unlikely(PageHuge(page))) + return hugetlb_basepage_index(page); return page_to_index(page); } --- a/kernel/futex.c~mm-futex-fix-shared-futex-pgoff-on-shmem-huge-page +++ a/kernel/futex.c @@ -35,7 +35,6 @@ #include <linux/jhash.h> #include <linux/pagemap.h> #include <linux/syscalls.h> -#include <linux/hugetlb.h> #include <linux/freezer.h> #include <linux/memblock.h> #include <linux/fault-inject.h> @@ -650,7 +649,7 @@ again: key->both.offset |= FUT_OFF_INODE; /* inode-based key */ key->shared.i_seq = get_inode_sequence_number(inode); - key->shared.pgoff = basepage_index(tail); + key->shared.pgoff = page_to_pgoff(tail); rcu_read_unlock(); } --- a/mm/hugetlb.c~mm-futex-fix-shared-futex-pgoff-on-shmem-huge-page +++ a/mm/hugetlb.c @@ -1588,15 +1588,12 @@ struct address_space *hugetlb_page_mappi return NULL; } -pgoff_t __basepage_index(struct page *page) +pgoff_t hugetlb_basepage_index(struct page *page) { struct page *page_head = compound_head(page); pgoff_t index = page_index(page_head); unsigned long compound_idx; - if (!PageHuge(page_head)) - return page_index(page); - if (compound_order(page_head) >= MAX_ORDER) compound_idx = page_to_pfn(page) - page_to_pfn(page_head); else _

3 years, 3 months

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[patch 16/24] kthread: prevent deadlock when kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync()

by Andrew Morton

From: Petr Mladek <pmladek(a)suse.com> Subject: kthread: prevent deadlock when kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync() The system might hang with the following backtrace: schedule+0x80/0x100 schedule_timeout+0x48/0x138 wait_for_common+0xa4/0x134 wait_for_completion+0x1c/0x2c kthread_flush_work+0x114/0x1cc kthread_cancel_work_sync.llvm.16514401384283632983+0xe8/0x144 kthread_cancel_delayed_work_sync+0x18/0x2c xxxx_pm_notify+0xb0/0xd8 blocking_notifier_call_chain_robust+0x80/0x194 pm_notifier_call_chain_robust+0x28/0x4c suspend_prepare+0x40/0x260 enter_state+0x80/0x3f4 pm_suspend+0x60/0xdc state_store+0x108/0x144 kobj_attr_store+0x38/0x88 sysfs_kf_write+0x64/0xc0 kernfs_fop_write_iter+0x108/0x1d0 vfs_write+0x2f4/0x368 ksys_write+0x7c/0xec It is caused by the following race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync(): CPU0 CPU1 Context: Thread A Context: Thread B kthread_mod_delayed_work() spin_lock() __kthread_cancel_work() spin_unlock() del_timer_sync() kthread_cancel_delayed_work_sync() spin_lock() __kthread_cancel_work() spin_unlock() del_timer_sync() spin_lock() work->canceling++ spin_unlock spin_lock() queue_delayed_work() // dwork is put into the worker->delayed_work_list spin_unlock() kthread_flush_work() // flush_work is put at the tail of the dwork wait_for_completion() Context: IRQ kthread_delayed_work_timer_fn() spin_lock() list_del_init(&work->node); spin_unlock() BANG: flush_work is not longer linked and will never get proceed. The problem is that kthread_mod_delayed_work() checks work->canceling flag before canceling the timer. A simple solution is to (re)check work->canceling after __kthread_cancel_work(). But then it is not clear what should be returned when __kthread_cancel_work() removed the work from the queue (list) and it can't queue it again with the new @delay. The return value might be used for reference counting. The caller has to know whether a new work has been queued or an existing one was replaced. The proper solution is that kthread_mod_delayed_work() will remove the work from the queue (list) _only_ when work->canceling is not set. The flag must be checked after the timer is stopped and the remaining operations can be done under worker->lock. Note that kthread_mod_delayed_work() could remove the timer and then bail out. It is fine. The other canceling caller needs to cancel the timer as well. The important thing is that the queue (list) manipulation is done atomically under worker->lock. Link: https://lkml.kernel.org/r/20210610133051.15337-3-pmladek@suse.com Fixes: 9a6b06c8d9a220860468a ("kthread: allow to modify delayed kthread work") Signed-off-by: Petr Mladek <pmladek(a)suse.com> Reported-by: Martin Liu <liumartin(a)google.com> Cc: <jenhaochen(a)google.com> Cc: Minchan Kim <minchan(a)google.com> Cc: Nathan Chancellor <nathan(a)kernel.org> Cc: Nick Desaulniers <ndesaulniers(a)google.com> Cc: Oleg Nesterov <oleg(a)redhat.com> Cc: Tejun Heo <tj(a)kernel.org> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- kernel/kthread.c | 35 ++++++++++++++++++++++++----------- 1 file changed, 24 insertions(+), 11 deletions(-) --- a/kernel/kthread.c~kthread-prevent-deadlock-when-kthread_mod_delayed_work-races-with-kthread_cancel_delayed_work_sync +++ a/kernel/kthread.c @@ -1120,8 +1120,11 @@ static void kthread_cancel_delayed_work_ } /* - * This function removes the work from the worker queue. Also it makes sure - * that it won't get queued later via the delayed work's timer. + * This function removes the work from the worker queue. + * + * It is called under worker->lock. The caller must make sure that + * the timer used by delayed work is not running, e.g. by calling + * kthread_cancel_delayed_work_timer(). * * The work might still be in use when this function finishes. See the * current_work proceed by the worker. @@ -1129,13 +1132,8 @@ static void kthread_cancel_delayed_work_ * Return: %true if @work was pending and successfully canceled, * %false if @work was not pending */ -static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork, - unsigned long *flags) +static bool __kthread_cancel_work(struct kthread_work *work) { - /* Try to cancel the timer if exists. */ - if (is_dwork) - kthread_cancel_delayed_work_timer(work, flags); - /* * Try to remove the work from a worker list. It might either * be from worker->work_list or from worker->delayed_work_list. @@ -1188,11 +1186,23 @@ bool kthread_mod_delayed_work(struct kth /* Work must not be used with >1 worker, see kthread_queue_work() */ WARN_ON_ONCE(work->worker != worker); - /* Do not fight with another command that is canceling this work. */ + /* + * Temporary cancel the work but do not fight with another command + * that is canceling the work as well. + * + * It is a bit tricky because of possible races with another + * mod_delayed_work() and cancel_delayed_work() callers. + * + * The timer must be canceled first because worker->lock is released + * when doing so. But the work can be removed from the queue (list) + * only when it can be queued again so that the return value can + * be used for reference counting. + */ + kthread_cancel_delayed_work_timer(work, &flags); if (work->canceling) goto out; + ret = __kthread_cancel_work(work); - ret = __kthread_cancel_work(work, true, &flags); fast_queue: __kthread_queue_delayed_work(worker, dwork, delay); out: @@ -1214,7 +1224,10 @@ static bool __kthread_cancel_work_sync(s /* Work must not be used with >1 worker, see kthread_queue_work(). */ WARN_ON_ONCE(work->worker != worker); - ret = __kthread_cancel_work(work, is_dwork, &flags); + if (is_dwork) + kthread_cancel_delayed_work_timer(work, &flags); + + ret = __kthread_cancel_work(work); if (worker->current_work != work) goto out_fast; _

3 years, 3 months

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[patch 15/24] kthread_worker: split code for canceling the delayed work timer

by Andrew Morton

From: Petr Mladek <pmladek(a)suse.com> Subject: kthread_worker: split code for canceling the delayed work timer Patch series "kthread_worker: Fix race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync()". This patchset fixes the race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync() including proper return value handling. This patch (of 2): Simple code refactoring as a preparation step for fixing a race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync(). It does not modify the existing behavior. Link: https://lkml.kernel.org/r/20210610133051.15337-2-pmladek@suse.com Signed-off-by: Petr Mladek <pmladek(a)suse.com> Cc: <jenhaochen(a)google.com> Cc: Martin Liu <liumartin(a)google.com> Cc: Minchan Kim <minchan(a)google.com> Cc: Nathan Chancellor <nathan(a)kernel.org> Cc: Nick Desaulniers <ndesaulniers(a)google.com> Cc: Oleg Nesterov <oleg(a)redhat.com> Cc: Tejun Heo <tj(a)kernel.org> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- kernel/kthread.c | 46 ++++++++++++++++++++++++++++----------------- 1 file changed, 29 insertions(+), 17 deletions(-) --- a/kernel/kthread.c~kthread_worker-split-code-for-canceling-the-delayed-work-timer +++ a/kernel/kthread.c @@ -1093,6 +1093,33 @@ void kthread_flush_work(struct kthread_w EXPORT_SYMBOL_GPL(kthread_flush_work); /* + * Make sure that the timer is neither set nor running and could + * not manipulate the work list_head any longer. + * + * The function is called under worker->lock. The lock is temporary + * released but the timer can't be set again in the meantime. + */ +static void kthread_cancel_delayed_work_timer(struct kthread_work *work, + unsigned long *flags) +{ + struct kthread_delayed_work *dwork = + container_of(work, struct kthread_delayed_work, work); + struct kthread_worker *worker = work->worker; + + /* + * del_timer_sync() must be called to make sure that the timer + * callback is not running. The lock must be temporary released + * to avoid a deadlock with the callback. In the meantime, + * any queuing is blocked by setting the canceling counter. + */ + work->canceling++; + raw_spin_unlock_irqrestore(&worker->lock, *flags); + del_timer_sync(&dwork->timer); + raw_spin_lock_irqsave(&worker->lock, *flags); + work->canceling--; +} + +/* * This function removes the work from the worker queue. Also it makes sure * that it won't get queued later via the delayed work's timer. * @@ -1106,23 +1133,8 @@ static bool __kthread_cancel_work(struct unsigned long *flags) { /* Try to cancel the timer if exists. */ - if (is_dwork) { - struct kthread_delayed_work *dwork = - container_of(work, struct kthread_delayed_work, work); - struct kthread_worker *worker = work->worker; - - /* - * del_timer_sync() must be called to make sure that the timer - * callback is not running. The lock must be temporary released - * to avoid a deadlock with the callback. In the meantime, - * any queuing is blocked by setting the canceling counter. - */ - work->canceling++; - raw_spin_unlock_irqrestore(&worker->lock, *flags); - del_timer_sync(&dwork->timer); - raw_spin_lock_irqsave(&worker->lock, *flags); - work->canceling--; - } + if (is_dwork) + kthread_cancel_delayed_work_timer(work, flags); /* * Try to remove the work from a worker list. It might either _

3 years, 3 months

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[patch 10/24] mm/thp: another PVMW_SYNC fix in page_vma_mapped_walk()

by Andrew Morton

From: Hugh Dickins <hughd(a)google.com> Subject: mm/thp: another PVMW_SYNC fix in page_vma_mapped_walk() Aha! Shouldn't that quick scan over pte_none()s make sure that it holds ptlock in the PVMW_SYNC case? That too might have been responsible for BUGs or WARNs in split_huge_page_to_list() or its unmap_page(), though I've never seen any. Link: https://lkml.kernel.org/r/1bdf384c-8137-a149-2a1e-475a4791c3c@google.com Link: https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@e16-tech.com/ Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()") Signed-off-by: Hugh Dickins <hughd(a)google.com> Acked-by: Kirill A. Shutemov <kirill.shutemov(a)linux.intel.com> Tested-by: Wang Yugui <wangyugui(a)e16-tech.com> Cc: Alistair Popple <apopple(a)nvidia.com> Cc: Matthew Wilcox <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Ralph Campbell <rcampbell(a)nvidia.com> Cc: Will Deacon <will(a)kernel.org> Cc: Yang Shi <shy828301(a)gmail.com> Cc: Zi Yan <ziy(a)nvidia.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/page_vma_mapped.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/mm/page_vma_mapped.c~mm-thp-another-pvmw_sync-fix-in-page_vma_mapped_walk +++ a/mm/page_vma_mapped.c @@ -276,6 +276,10 @@ next_pte: goto restart; } pvmw->pte++; + if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) { + pvmw->ptl = pte_lockptr(mm, pvmw->pmd); + spin_lock(pvmw->ptl); + } } while (pte_none(*pvmw->pte)); if (!pvmw->ptl) { _

3 years, 3 months

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[patch 09/24] mm/thp: fix page_vma_mapped_walk() if THP mapped by ptes

by Andrew Morton

From: Hugh Dickins <hughd(a)google.com> Subject: mm/thp: fix page_vma_mapped_walk() if THP mapped by ptes Running certain tests with a DEBUG_VM kernel would crash within hours, on the total_mapcount BUG() in split_huge_page_to_list(), while trying to free up some memory by punching a hole in a shmem huge page: split's try_to_unmap() was unable to find all the mappings of the page (which, on a !DEBUG_VM kernel, would then keep the huge page pinned in memory). Crash dumps showed two tail pages of a shmem huge page remained mapped by pte: ptes in a non-huge-aligned vma of a gVisor process, at the end of a long unmapped range; and no page table had yet been allocated for the head of the huge page to be mapped into. Although designed to handle these odd misaligned huge-page-mapped-by-pte cases, page_vma_mapped_walk() falls short by returning false prematurely when !pmd_present or !pud_present or !p4d_present or !pgd_present: there are cases when a huge page may span the boundary, with ptes present in the next. Restructure page_vma_mapped_walk() as a loop to continue in these cases, while keeping its layout much as before. Add a step_forward() helper to advance pvmw->address across those boundaries: originally I tried to use mm's standard p?d_addr_end() macros, but hit the same crash 512 times less often: because of the way redundant levels are folded together, but folded differently in different configurations, it was just too difficult to use them correctly; and step_forward() is simpler anyway. Link: https://lkml.kernel.org/r/fedb8632-1798-de42-f39e-873551d5bc81@google.com Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()") Signed-off-by: Hugh Dickins <hughd(a)google.com> Acked-by: Kirill A. Shutemov <kirill.shutemov(a)linux.intel.com> Cc: Alistair Popple <apopple(a)nvidia.com> Cc: Matthew Wilcox <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Ralph Campbell <rcampbell(a)nvidia.com> Cc: Wang Yugui <wangyugui(a)e16-tech.com> Cc: Will Deacon <will(a)kernel.org> Cc: Yang Shi <shy828301(a)gmail.com> Cc: Zi Yan <ziy(a)nvidia.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/page_vma_mapped.c | 34 +++++++++++++++++++++++++--------- 1 file changed, 25 insertions(+), 9 deletions(-) --- a/mm/page_vma_mapped.c~mm-thp-fix-page_vma_mapped_walk-if-thp-mapped-by-ptes +++ a/mm/page_vma_mapped.c @@ -116,6 +116,13 @@ static bool check_pte(struct page_vma_ma return pfn_is_match(pvmw->page, pfn); } +static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size) +{ + pvmw->address = (pvmw->address + size) & ~(size - 1); + if (!pvmw->address) + pvmw->address = ULONG_MAX; +} + /** * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at * @pvmw->address @@ -183,16 +190,22 @@ bool page_vma_mapped_walk(struct page_vm if (pvmw->pte) goto next_pte; restart: - { + do { pgd = pgd_offset(mm, pvmw->address); - if (!pgd_present(*pgd)) - return false; + if (!pgd_present(*pgd)) { + step_forward(pvmw, PGDIR_SIZE); + continue; + } p4d = p4d_offset(pgd, pvmw->address); - if (!p4d_present(*p4d)) - return false; + if (!p4d_present(*p4d)) { + step_forward(pvmw, P4D_SIZE); + continue; + } pud = pud_offset(p4d, pvmw->address); - if (!pud_present(*pud)) - return false; + if (!pud_present(*pud)) { + step_forward(pvmw, PUD_SIZE); + continue; + } pvmw->pmd = pmd_offset(pud, pvmw->address); /* @@ -239,7 +252,8 @@ restart: spin_unlock(ptl); } - return false; + step_forward(pvmw, PMD_SIZE); + continue; } if (!map_pte(pvmw)) goto next_pte; @@ -269,7 +283,9 @@ next_pte: spin_lock(pvmw->ptl); } goto this_pte; - } + } while (pvmw->address < end); + + return false; } /** _

3 years, 3 months

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[patch 08/24] mm: page_vma_mapped_walk(): get vma_address_end() earlier

by Andrew Morton

From: Hugh Dickins <hughd(a)google.com> Subject: mm: page_vma_mapped_walk(): get vma_address_end() earlier page_vma_mapped_walk() cleanup: get THP's vma_address_end() at the start, rather than later at next_pte. It's a little unnecessary overhead on the first call, but makes for a simpler loop in the following commit. Link: https://lkml.kernel.org/r/4542b34d-862f-7cb4-bb22-e0df6ce830a2@google.com Signed-off-by: Hugh Dickins <hughd(a)google.com> Acked-by: Kirill A. Shutemov <kirill.shutemov(a)linux.intel.com> Cc: Alistair Popple <apopple(a)nvidia.com> Cc: Matthew Wilcox <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Ralph Campbell <rcampbell(a)nvidia.com> Cc: Wang Yugui <wangyugui(a)e16-tech.com> Cc: Will Deacon <will(a)kernel.org> Cc: Yang Shi <shy828301(a)gmail.com> Cc: Zi Yan <ziy(a)nvidia.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/page_vma_mapped.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) --- a/mm/page_vma_mapped.c~mm-page_vma_mapped_walk-get-vma_address_end-earlier +++ a/mm/page_vma_mapped.c @@ -171,6 +171,15 @@ bool page_vma_mapped_walk(struct page_vm return true; } + /* + * Seek to next pte only makes sense for THP. + * But more important than that optimization, is to filter out + * any PageKsm page: whose page->index misleads vma_address() + * and vma_address_end() to disaster. + */ + end = PageTransCompound(page) ? + vma_address_end(page, pvmw->vma) : + pvmw->address + PAGE_SIZE; if (pvmw->pte) goto next_pte; restart: @@ -238,10 +247,6 @@ this_pte: if (check_pte(pvmw)) return true; next_pte: - /* Seek to next pte only makes sense for THP */ - if (!PageTransHuge(page)) - return not_found(pvmw); - end = vma_address_end(page, pvmw->vma); do { pvmw->address += PAGE_SIZE; if (pvmw->address >= end) _

3 years, 3 months

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[patch 07/24] mm: page_vma_mapped_walk(): use goto instead of while (1)

by Andrew Morton

From: Hugh Dickins <hughd(a)google.com> Subject: mm: page_vma_mapped_walk(): use goto instead of while (1) page_vma_mapped_walk() cleanup: add a label this_pte, matching next_pte, and use "goto this_pte", in place of the "while (1)" loop at the end. Link: https://lkml.kernel.org/r/a52b234a-851-3616-2525-f42736e8934@google.com Signed-off-by: Hugh Dickins <hughd(a)google.com> Acked-by: Kirill A. Shutemov <kirill.shutemov(a)linux.intel.com> Cc: Alistair Popple <apopple(a)nvidia.com> Cc: Matthew Wilcox <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Ralph Campbell <rcampbell(a)nvidia.com> Cc: Wang Yugui <wangyugui(a)e16-tech.com> Cc: Will Deacon <will(a)kernel.org> Cc: Yang Shi <shy828301(a)gmail.com> Cc: Zi Yan <ziy(a)nvidia.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/page_vma_mapped.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) --- a/mm/page_vma_mapped.c~mm-page_vma_mapped_walk-use-goto-instead-of-while-1 +++ a/mm/page_vma_mapped.c @@ -144,6 +144,7 @@ bool page_vma_mapped_walk(struct page_vm { struct mm_struct *mm = pvmw->vma->vm_mm; struct page *page = pvmw->page; + unsigned long end; pgd_t *pgd; p4d_t *p4d; pud_t *pud; @@ -233,10 +234,7 @@ restart: } if (!map_pte(pvmw)) goto next_pte; - } - while (1) { - unsigned long end; - +this_pte: if (check_pte(pvmw)) return true; next_pte: @@ -265,6 +263,7 @@ next_pte: pvmw->ptl = pte_lockptr(mm, pvmw->pmd); spin_lock(pvmw->ptl); } + goto this_pte; } } _

3 years, 3 months

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[patch 06/24] mm: page_vma_mapped_walk(): add a level of indentation

by Andrew Morton

From: Hugh Dickins <hughd(a)google.com> Subject: mm: page_vma_mapped_walk(): add a level of indentation page_vma_mapped_walk() cleanup: add a level of indentation to much of the body, making no functional change in this commit, but reducing the later diff when this is all converted to a loop. [hughd(a)google.com: : page_vma_mapped_walk(): add a level of indentation fix] Link: https://lkml.kernel.org/r/7f817555-3ce1-c785-e438-87d8efdcaf26@google.com Link: https://lkml.kernel.org/r/efde211-f3e2-fe54-977-ef481419e7f3@google.com Signed-off-by: Hugh Dickins <hughd(a)google.com> Acked-by: Kirill A. Shutemov <kirill.shutemov(a)linux.intel.com> Cc: Alistair Popple <apopple(a)nvidia.com> Cc: Matthew Wilcox <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Ralph Campbell <rcampbell(a)nvidia.com> Cc: Wang Yugui <wangyugui(a)e16-tech.com> Cc: Will Deacon <will(a)kernel.org> Cc: Yang Shi <shy828301(a)gmail.com> Cc: Zi Yan <ziy(a)nvidia.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/page_vma_mapped.c | 105 +++++++++++++++++++++-------------------- 1 file changed, 55 insertions(+), 50 deletions(-) --- a/mm/page_vma_mapped.c~mm-page_vma_mapped_walk-add-a-level-of-indentation +++ a/mm/page_vma_mapped.c @@ -173,62 +173,67 @@ bool page_vma_mapped_walk(struct page_vm if (pvmw->pte) goto next_pte; restart: - pgd = pgd_offset(mm, pvmw->address); - if (!pgd_present(*pgd)) - return false; - p4d = p4d_offset(pgd, pvmw->address); - if (!p4d_present(*p4d)) - return false; - pud = pud_offset(p4d, pvmw->address); - if (!pud_present(*pud)) - return false; - pvmw->pmd = pmd_offset(pud, pvmw->address); - /* - * Make sure the pmd value isn't cached in a register by the - * compiler and used as a stale value after we've observed a - * subsequent update. - */ - pmde = READ_ONCE(*pvmw->pmd); - if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) { - pvmw->ptl = pmd_lock(mm, pvmw->pmd); - pmde = *pvmw->pmd; - if (likely(pmd_trans_huge(pmde))) { - if (pvmw->flags & PVMW_MIGRATION) - return not_found(pvmw); - if (pmd_page(pmde) != page) - return not_found(pvmw); - return true; - } - if (!pmd_present(pmde)) { - swp_entry_t entry; + { + pgd = pgd_offset(mm, pvmw->address); + if (!pgd_present(*pgd)) + return false; + p4d = p4d_offset(pgd, pvmw->address); + if (!p4d_present(*p4d)) + return false; + pud = pud_offset(p4d, pvmw->address); + if (!pud_present(*pud)) + return false; - if (!thp_migration_supported() || - !(pvmw->flags & PVMW_MIGRATION)) - return not_found(pvmw); - entry = pmd_to_swp_entry(pmde); - if (!is_migration_entry(entry) || - migration_entry_to_page(entry) != page) - return not_found(pvmw); - return true; - } - /* THP pmd was split under us: handle on pte level */ - spin_unlock(pvmw->ptl); - pvmw->ptl = NULL; - } else if (!pmd_present(pmde)) { + pvmw->pmd = pmd_offset(pud, pvmw->address); /* - * If PVMW_SYNC, take and drop THP pmd lock so that we - * cannot return prematurely, while zap_huge_pmd() has - * cleared *pmd but not decremented compound_mapcount(). + * Make sure the pmd value isn't cached in a register by the + * compiler and used as a stale value after we've observed a + * subsequent update. */ - if ((pvmw->flags & PVMW_SYNC) && PageTransCompound(page)) { - spinlock_t *ptl = pmd_lock(mm, pvmw->pmd); + pmde = READ_ONCE(*pvmw->pmd); + + if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) { + pvmw->ptl = pmd_lock(mm, pvmw->pmd); + pmde = *pvmw->pmd; + if (likely(pmd_trans_huge(pmde))) { + if (pvmw->flags & PVMW_MIGRATION) + return not_found(pvmw); + if (pmd_page(pmde) != page) + return not_found(pvmw); + return true; + } + if (!pmd_present(pmde)) { + swp_entry_t entry; - spin_unlock(ptl); + if (!thp_migration_supported() || + !(pvmw->flags & PVMW_MIGRATION)) + return not_found(pvmw); + entry = pmd_to_swp_entry(pmde); + if (!is_migration_entry(entry) || + migration_entry_to_page(entry) != page) + return not_found(pvmw); + return true; + } + /* THP pmd was split under us: handle on pte level */ + spin_unlock(pvmw->ptl); + pvmw->ptl = NULL; + } else if (!pmd_present(pmde)) { + /* + * If PVMW_SYNC, take and drop THP pmd lock so that we + * cannot return prematurely, while zap_huge_pmd() has + * cleared *pmd but not decremented compound_mapcount(). + */ + if ((pvmw->flags & PVMW_SYNC) && + PageTransCompound(page)) { + spinlock_t *ptl = pmd_lock(mm, pvmw->pmd); + + spin_unlock(ptl); + } + return false; } - return false; + if (!map_pte(pvmw)) + goto next_pte; } - if (!map_pte(pvmw)) - goto next_pte; while (1) { unsigned long end; _

3 years, 3 months

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