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Date:      Wed, 30 Jul 2014 14:14:46 -0500
From:      Alan Cox <alc@rice.edu>
To:        Andreas Tobler <andreast@FreeBSD.org>, Alan Cox <alc@FreeBSD.org>, src-committers@FreeBSD.org, svn-src-all@FreeBSD.org, svn-src-head@FreeBSD.org
Subject:   Re: svn commit: r269134 - head/sys/vm
Message-ID:  <53D94426.3010301@rice.edu>
In-Reply-To: <53D9406A.3060101@FreeBSD.org>
References:  <201407261810.s6QIAIIj049439@svn.freebsd.org> <53D9406A.3060101@FreeBSD.org>

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On 07/30/2014 13:58, Andreas Tobler wrote:
> Hi Alan,
>
> On 26.07.14 20:10, Alan Cox wrote:
>> Author: alc
>> Date: Sat Jul 26 18:10:18 2014
>> New Revision: 269134
>> URL: http://svnweb.freebsd.org/changeset/base/269134
>>
>> Log:
>>    When unwiring a region of an address space, do not assume that the
>>    underlying physical pages are mapped by the pmap.  If, for
>> example, the
>>    application has performed an mprotect(..., PROT_NONE) on any part
>> of the
>>    wired region, then those pages will no longer be mapped by the pmap.
>>    So, using the pmap to lookup the wired pages in order to unwire them
>>    doesn't always work, and when it doesn't work wired pages are leaked.
>>
>>    To avoid the leak, introduce and use a new function
>> vm_object_unwire()
>>    that locates the wired pages by traversing the object and its backing
>>    objects.
>>
>>    At the same time, switch from using pmap_change_wiring() to the
>> recently
>>    introduced function pmap_unwire() for unwiring the region's mappings.
>>    pmap_unwire() is faster, because it operates a range of virtual
>> addresses
>>    rather than a single virtual page at a time.  Moreover, by
>> operating on
>>    a range, it is superpage friendly.  It doesn't waste time performing
>>    unnecessary demotions.
>>
>>    Reported by:    markj
>>    Reviewed by:    kib
>>    Tested by:    pho, jmg (arm)
>>    Sponsored by:    EMC / Isilon Storage Division
>
> This commit brings my 32- and 64-bit PowerMac's into panic.
> Unfortunately I'm not able to give you a backtrace in the form of a
> textdump nor of a core dump.
>
> The only thing I have is this picture:
>
> http://people.freebsd.org/~andreast/r269134_panic.jpg
>
> Exactly this revision gives a panic and breaks the textdump/coredump
> facility.
>
> How can I help debugging?
>


For now, that's all I need to know.


>
>>
>> Modified:
>>    head/sys/vm/vm_extern.h
>>    head/sys/vm/vm_fault.c
>>    head/sys/vm/vm_map.c
>>    head/sys/vm/vm_object.c
>>    head/sys/vm/vm_object.h
>>
>> Modified: head/sys/vm/vm_extern.h
>> ==============================================================================
>>
>> --- head/sys/vm/vm_extern.h    Sat Jul 26 17:59:25 2014    (r269133)
>> +++ head/sys/vm/vm_extern.h    Sat Jul 26 18:10:18 2014    (r269134)
>> @@ -81,7 +81,6 @@ int vm_fault_hold(vm_map_t map, vm_offse
>>       int fault_flags, vm_page_t *m_hold);
>>   int vm_fault_quick_hold_pages(vm_map_t map, vm_offset_t addr,
>> vm_size_t len,
>>       vm_prot_t prot, vm_page_t *ma, int max_count);
>> -void vm_fault_unwire(vm_map_t, vm_offset_t, vm_offset_t, boolean_t);
>>   int vm_fault_wire(vm_map_t, vm_offset_t, vm_offset_t, boolean_t);
>>   int vm_forkproc(struct thread *, struct proc *, struct thread *,
>> struct vmspace *, int);
>>   void vm_waitproc(struct proc *);
>>
>> Modified: head/sys/vm/vm_fault.c
>> ==============================================================================
>>
>> --- head/sys/vm/vm_fault.c    Sat Jul 26 17:59:25 2014    (r269133)
>> +++ head/sys/vm/vm_fault.c    Sat Jul 26 18:10:18 2014    (r269134)
>> @@ -106,6 +106,7 @@ __FBSDID("$FreeBSD$");
>>   #define PFFOR 4
>>
>>   static int vm_fault_additional_pages(vm_page_t, int, int, vm_page_t
>> *, int *);
>> +static void vm_fault_unwire(vm_map_t, vm_offset_t, vm_offset_t,
>> boolean_t);
>>
>>   #define    VM_FAULT_READ_BEHIND    8
>>   #define    VM_FAULT_READ_MAX    (1 + VM_FAULT_READ_AHEAD_MAX)
>> @@ -1186,7 +1187,7 @@ vm_fault_wire(vm_map_t map, vm_offset_t
>>    *
>>    *    Unwire a range of virtual addresses in a map.
>>    */
>> -void
>> +static void
>>   vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
>>       boolean_t fictitious)
>>   {
>>
>> Modified: head/sys/vm/vm_map.c
>> ==============================================================================
>>
>> --- head/sys/vm/vm_map.c    Sat Jul 26 17:59:25 2014    (r269133)
>> +++ head/sys/vm/vm_map.c    Sat Jul 26 18:10:18 2014    (r269134)
>> @@ -132,6 +132,7 @@ static void _vm_map_init(vm_map_t map, p
>>       vm_offset_t max);
>>   static void vm_map_entry_deallocate(vm_map_entry_t entry, boolean_t
>> system_map);
>>   static void vm_map_entry_dispose(vm_map_t map, vm_map_entry_t entry);
>> +static void vm_map_entry_unwire(vm_map_t map, vm_map_entry_t entry);
>>   #ifdef INVARIANTS
>>   static void vm_map_zdtor(void *mem, int size, void *arg);
>>   static void vmspace_zdtor(void *mem, int size, void *arg);
>> @@ -2393,16 +2394,10 @@ done:
>>               (entry->eflags & MAP_ENTRY_USER_WIRED))) {
>>               if (user_unwire)
>>                   entry->eflags &= ~MAP_ENTRY_USER_WIRED;
>> -            entry->wired_count--;
>> -            if (entry->wired_count == 0) {
>> -                /*
>> -                 * Retain the map lock.
>> -                 */
>> -                vm_fault_unwire(map, entry->start, entry->end,
>> -                    entry->object.vm_object != NULL &&
>> -                    (entry->object.vm_object->flags &
>> -                    OBJ_FICTITIOUS) != 0);
>> -            }
>> +            if (entry->wired_count == 1)
>> +                vm_map_entry_unwire(map, entry);
>> +            else
>> +                entry->wired_count--;
>>           }
>>           KASSERT((entry->eflags & MAP_ENTRY_IN_TRANSITION) != 0,
>>               ("vm_map_unwire: in-transition flag missing %p", entry));
>> @@ -2635,19 +2630,12 @@ done:
>>                * unnecessary.
>>                */
>>               entry->wired_count = 0;
>> -        } else {
>> -            if (!user_wire ||
>> -                (entry->eflags & MAP_ENTRY_USER_WIRED) == 0)
>> +        } else if (!user_wire ||
>> +            (entry->eflags & MAP_ENTRY_USER_WIRED) == 0) {
>> +            if (entry->wired_count == 1)
>> +                vm_map_entry_unwire(map, entry);
>> +            else
>>                   entry->wired_count--;
>> -            if (entry->wired_count == 0) {
>> -                /*
>> -                 * Retain the map lock.
>> -                 */
>> -                vm_fault_unwire(map, entry->start, entry->end,
>> -                    entry->object.vm_object != NULL &&
>> -                    (entry->object.vm_object->flags &
>> -                    OBJ_FICTITIOUS) != 0);
>> -            }
>>           }
>>       next_entry_done:
>>           KASSERT((entry->eflags & MAP_ENTRY_IN_TRANSITION) != 0,
>> @@ -2783,9 +2771,13 @@ vm_map_sync(
>>   static void
>>   vm_map_entry_unwire(vm_map_t map, vm_map_entry_t entry)
>>   {
>> -    vm_fault_unwire(map, entry->start, entry->end,
>> -        entry->object.vm_object != NULL &&
>> -        (entry->object.vm_object->flags & OBJ_FICTITIOUS) != 0);
>> +
>> +    VM_MAP_ASSERT_LOCKED(map);
>> +    KASSERT(entry->wired_count > 0,
>> +        ("vm_map_entry_unwire: entry %p isn't wired", entry));
>> +    pmap_unwire(map->pmap, entry->start, entry->end);
>> +    vm_object_unwire(entry->object.vm_object, entry->offset,
>> entry->end -
>> +        entry->start, PQ_ACTIVE);
>>       entry->wired_count = 0;
>>   }
>>
>>
>> Modified: head/sys/vm/vm_object.c
>> ==============================================================================
>>
>> --- head/sys/vm/vm_object.c    Sat Jul 26 17:59:25 2014    (r269133)
>> +++ head/sys/vm/vm_object.c    Sat Jul 26 18:10:18 2014    (r269134)
>> @@ -2202,6 +2202,78 @@ vm_object_set_writeable_dirty(vm_object_
>>       vm_object_set_flag(object, OBJ_MIGHTBEDIRTY);
>>   }
>>
>> +/*
>> + *    vm_object_unwire:
>> + *
>> + *    For each page offset within the specified range of the given
>> object,
>> + *    find the highest-level page in the shadow chain and unwire
>> it.  A page
>> + *    must exist at every page offset, and the highest-level page
>> must be
>> + *    wired.
>> + */
>> +void
>> +vm_object_unwire(vm_object_t object, vm_ooffset_t offset, vm_size_t
>> length,
>> +    uint8_t queue)
>> +{
>> +    vm_object_t tobject;
>> +    vm_page_t m, tm;
>> +    vm_pindex_t end_pindex, pindex, tpindex;
>> +    int depth, locked_depth;
>> +
>> +    KASSERT((offset & PAGE_MASK) == 0,
>> +        ("vm_object_unwire: offset is not page aligned"));
>> +    KASSERT((length & PAGE_MASK) == 0,
>> +        ("vm_object_unwire: length is not a multiple of PAGE_SIZE"));
>> +    /* The wired count of a fictitious page never changes. */
>> +    if ((object->flags & OBJ_FICTITIOUS) != 0)
>> +        return;
>> +    pindex = OFF_TO_IDX(offset);
>> +    end_pindex = pindex + atop(length);
>> +    locked_depth = 1;
>> +    VM_OBJECT_RLOCK(object);
>> +    m = vm_page_find_least(object, pindex);
>> +    while (pindex < end_pindex) {
>> +        if (m == NULL || pindex < m->pindex) {
>> +            /*
>> +             * The first object in the shadow chain doesn't
>> +             * contain a page at the current index.  Therefore,
>> +             * the page must exist in a backing object.
>> +             */
>> +            tobject = object;
>> +            tpindex = pindex;
>> +            depth = 0;
>> +            do {
>> +                tpindex +=
>> +                    OFF_TO_IDX(tobject->backing_object_offset);
>> +                tobject = tobject->backing_object;
>> +                KASSERT(tobject != NULL,
>> +                    ("vm_object_unwire: missing page"));
>> +                if ((tobject->flags & OBJ_FICTITIOUS) != 0)
>> +                    goto next_page;
>> +                depth++;
>> +                if (depth == locked_depth) {
>> +                    locked_depth++;
>> +                    VM_OBJECT_RLOCK(tobject);
>> +                }
>> +            } while ((tm = vm_page_lookup(tobject, tpindex)) ==
>> +                NULL);
>> +        } else {
>> +            tm = m;
>> +            m = TAILQ_NEXT(m, listq);
>> +        }
>> +        vm_page_lock(tm);
>> +        vm_page_unwire(tm, queue);
>> +        vm_page_unlock(tm);
>> +next_page:
>> +        pindex++;
>> +    }
>> +    /* Release the accumulated object locks. */
>> +    for (depth = 0; depth < locked_depth; depth++) {
>> +        tobject = object->backing_object;
>> +        VM_OBJECT_RUNLOCK(object);
>> +        object = tobject;
>> +    }
>> +}
>> +
>>   #include "opt_ddb.h"
>>   #ifdef DDB
>>   #include <sys/kernel.h>
>>
>> Modified: head/sys/vm/vm_object.h
>> ==============================================================================
>>
>> --- head/sys/vm/vm_object.h    Sat Jul 26 17:59:25 2014    (r269133)
>> +++ head/sys/vm/vm_object.h    Sat Jul 26 18:10:18 2014    (r269134)
>> @@ -291,6 +291,8 @@ void vm_object_shadow (vm_object_t *, vm
>>   void vm_object_split(vm_map_entry_t);
>>   boolean_t vm_object_sync(vm_object_t, vm_ooffset_t, vm_size_t,
>> boolean_t,
>>       boolean_t);
>> +void vm_object_unwire(vm_object_t object, vm_ooffset_t offset,
>> +    vm_size_t length, uint8_t queue);
>>   #endif                /* _KERNEL */
>>
>>   #endif                /* _VM_OBJECT_ */
>>
>>
>>
>
>




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