| Message ID | 20200424013958.GC158937@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | None | expand |
On 4/24/20 3:39 AM, Michel Lespinasse wrote: > Rename the mmap_sem field to mmap_lock. Any new uses of this lock > should now go through the new mmap locking api. The mmap_lock is > still implemented as a rwsem, though this could change in the future. > > Signed-off-by: Michel Lespinasse <walken@google.com> Except gpu/drm/etnaviv/etnaviv_gem.c all direct users remain in mm or arch/fault code so that seems fine. Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Any plan about all the code comments mentioning mmap_sem? :) Not urgent.
Le 24/04/2020 à 03:39, Michel Lespinasse a écrit : > Rename the mmap_sem field to mmap_lock. Any new uses of this lock > should now go through the new mmap locking api. The mmap_lock is > still implemented as a rwsem, though this could change in the future. > > Signed-off-by: Michel Lespinasse <walken@google.com> > --- > arch/ia64/mm/fault.c | 4 +-- > arch/x86/mm/fault.c | 2 +- > drivers/gpu/drm/etnaviv/etnaviv_gem.c | 2 +- > include/linux/mm_types.h | 2 +- > include/linux/mmap_lock.h | 38 +++++++++++++-------------- > mm/memory.c | 2 +- > mm/mmap.c | 4 +-- > mm/mmu_notifier.c | 2 +- > 8 files changed, 28 insertions(+), 28 deletions(-) > > diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c > index 693f00b117e1..9b95050c2048 100644 > --- a/arch/ia64/mm/fault.c > +++ b/arch/ia64/mm/fault.c > @@ -70,8 +70,8 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re > mask = ((((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT) > | (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT)); > > - /* mmap_sem is performance critical.... */ > - prefetchw(&mm->mmap_sem); > + /* mmap_lock is performance critical.... */ > + prefetchw(&mm->mmap_lock); > > /* > * If we're in an interrupt or have no user context, we must not take the fault.. > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > index 181f66b9049f..35f530f9dfc0 100644 > --- a/arch/x86/mm/fault.c > +++ b/arch/x86/mm/fault.c > @@ -1522,7 +1522,7 @@ dotraplinkage void > do_page_fault(struct pt_regs *regs, unsigned long hw_error_code, > unsigned long address) > { > - prefetchw(¤t->mm->mmap_sem); > + prefetchw(¤t->mm->mmap_lock); > trace_page_fault_entries(regs, hw_error_code, address); > > if (unlikely(kmmio_fault(regs, address))) > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c > index dc9ef302f517..701f3995f621 100644 > --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c > @@ -661,7 +661,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj) > struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr; > int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT; > > - might_lock_read(¤t->mm->mmap_sem); > + might_lock_read(¤t->mm->mmap_lock); Why not a mm_might_lock_read() new API to hide the mmap_lock, and add it to the previous patch? > > if (userptr->mm != current->mm) > return -EPERM; > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 4aba6c0c2ba8..d13b90399c16 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -436,7 +436,7 @@ struct mm_struct { > spinlock_t page_table_lock; /* Protects page tables and some > * counters > */ > - struct rw_semaphore mmap_sem; > + struct rw_semaphore mmap_lock; > > struct list_head mmlist; /* List of maybe swapped mm's. These > * are globally strung together off > diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h > index 5bf7cee5d93b..9dc632add390 100644 > --- a/include/linux/mmap_lock.h > +++ b/include/linux/mmap_lock.h > @@ -4,67 +4,67 @@ > #include <linux/mmdebug.h> > > #define MMAP_LOCK_INITIALIZER(name) \ > - .mmap_sem = __RWSEM_INITIALIZER(name.mmap_sem), > + .mmap_lock = __RWSEM_INITIALIZER(name.mmap_lock), > > static inline void mmap_init_lock(struct mm_struct *mm) > { > - init_rwsem(&mm->mmap_sem); > + init_rwsem(&mm->mmap_lock); > } > > static inline void mmap_write_lock(struct mm_struct *mm) > { > - down_write(&mm->mmap_sem); > + down_write(&mm->mmap_lock); > } > > static inline void mmap_write_lock_nested(struct mm_struct *mm, int subclass) > { > - down_write_nested(&mm->mmap_sem, subclass); > + down_write_nested(&mm->mmap_lock, subclass); > } > > static inline int mmap_write_lock_killable(struct mm_struct *mm) > { > - return down_write_killable(&mm->mmap_sem); > + return down_write_killable(&mm->mmap_lock); > } > > static inline bool mmap_write_trylock(struct mm_struct *mm) > { > - return down_write_trylock(&mm->mmap_sem) != 0; > + return down_write_trylock(&mm->mmap_lock) != 0; > } > > static inline void mmap_write_unlock(struct mm_struct *mm) > { > - up_write(&mm->mmap_sem); > + up_write(&mm->mmap_lock); > } > > static inline void mmap_write_downgrade(struct mm_struct *mm) > { > - downgrade_write(&mm->mmap_sem); > + downgrade_write(&mm->mmap_lock); > } > > static inline void mmap_read_lock(struct mm_struct *mm) > { > - down_read(&mm->mmap_sem); > + down_read(&mm->mmap_lock); > } > > static inline int mmap_read_lock_killable(struct mm_struct *mm) > { > - return down_read_killable(&mm->mmap_sem); > + return down_read_killable(&mm->mmap_lock); > } > > static inline bool mmap_read_trylock(struct mm_struct *mm) > { > - return down_read_trylock(&mm->mmap_sem) != 0; > + return down_read_trylock(&mm->mmap_lock) != 0; > } > > static inline void mmap_read_unlock(struct mm_struct *mm) > { > - up_read(&mm->mmap_sem); > + up_read(&mm->mmap_lock); > } > > static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm) > { > - if (down_read_trylock(&mm->mmap_sem)) { > - rwsem_release(&mm->mmap_sem.dep_map, _RET_IP_); > + if (down_read_trylock(&mm->mmap_lock)) { > + rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_); > return true; > } > return false; > @@ -72,19 +72,19 @@ static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm) > > static inline void mmap_read_unlock_non_owner(struct mm_struct *mm) > { > - up_read_non_owner(&mm->mmap_sem); > + up_read_non_owner(&mm->mmap_lock); > } > > static inline void mmap_assert_locked(struct mm_struct *mm) > { > - VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_sem, -1), mm); > - VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm); > + VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_lock, -1), mm); > + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); > } > > static inline void mmap_assert_write_locked(struct mm_struct *mm) > { > - VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_sem, 0), mm); > - VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm); > + VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_lock, 0), mm); > + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); > } > > #endif /* _LINUX_MMAP_LOCK_H */ > diff --git a/mm/memory.c b/mm/memory.c > index 20f98ea8968e..c2963e7affa9 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4811,7 +4811,7 @@ void __might_fault(const char *file, int line) > __might_sleep(file, line, 0); > #if defined(CONFIG_DEBUG_ATOMIC_SLEEP) > if (current->mm) > - might_lock_read(¤t->mm->mmap_sem); > + might_lock_read(¤t->mm->mmap_lock); > #endif > } > EXPORT_SYMBOL(__might_fault); > diff --git a/mm/mmap.c b/mm/mmap.c > index 2f4ffccc5972..80a47031d5db 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -3474,7 +3474,7 @@ static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma) > * The LSB of head.next can't change from under us > * because we hold the mm_all_locks_mutex. > */ > - down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_sem); > + down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_lock); > /* > * We can safely modify head.next after taking the > * anon_vma->root->rwsem. If some other vma in this mm shares > @@ -3504,7 +3504,7 @@ static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping) > */ > if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags)) > BUG(); > - down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_sem); > + down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_lock); > } > } > > diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c > index 24eb9d1ed0a7..2f348b6c9c9a 100644 > --- a/mm/mmu_notifier.c > +++ b/mm/mmu_notifier.c > @@ -983,7 +983,7 @@ int mmu_interval_notifier_insert(struct mmu_interval_notifier *interval_sub, > struct mmu_notifier_subscriptions *subscriptions; > int ret; > > - might_lock(&mm->mmap_sem); > + might_lock(&mm->mmap_lock); Same here with a new mm_might_lock()? > > subscriptions = smp_load_acquire(&mm->notifier_subscriptions); > if (!subscriptions || !subscriptions->has_itree) { >
On Mon, May 18, 2020 at 03:45:22PM +0200, Laurent Dufour wrote: > Le 24/04/2020 à 03:39, Michel Lespinasse a écrit : > > Rename the mmap_sem field to mmap_lock. Any new uses of this lock > > should now go through the new mmap locking api. The mmap_lock is > > still implemented as a rwsem, though this could change in the future. > > > > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c > > index dc9ef302f517..701f3995f621 100644 > > --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c > > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c > > @@ -661,7 +661,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj) > > struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr; > > int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT; > > - might_lock_read(¤t->mm->mmap_sem); > > + might_lock_read(¤t->mm->mmap_lock); > > Why not a mm_might_lock_read() new API to hide the mmap_lock, and add it to > the previous patch? I'm not sure why this is needed - we may rework the lock to be something else than rwsem, but might_lock_read should still apply to it and make sense ? I'm not sure what the extra API would bring...
On Mon, May 18, 2020 at 01:07:26PM +0200, Vlastimil Babka wrote:
> Any plan about all the code comments mentioning mmap_sem? :) Not urgent.
It's mostly a sed job, I'll add it in the next version as it seems
the patchset is getting ready for inclusion.
Le 19/05/2020 à 15:10, Michel Lespinasse a écrit : > On Mon, May 18, 2020 at 03:45:22PM +0200, Laurent Dufour wrote: >> Le 24/04/2020 à 03:39, Michel Lespinasse a écrit : >>> Rename the mmap_sem field to mmap_lock. Any new uses of this lock >>> should now go through the new mmap locking api. The mmap_lock is >>> still implemented as a rwsem, though this could change in the future. >>> >>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c >>> index dc9ef302f517..701f3995f621 100644 >>> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c >>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c >>> @@ -661,7 +661,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj) >>> struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr; >>> int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT; >>> - might_lock_read(¤t->mm->mmap_sem); >>> + might_lock_read(¤t->mm->mmap_lock); >> >> Why not a mm_might_lock_read() new API to hide the mmap_lock, and add it to >> the previous patch? > > I'm not sure why this is needed - we may rework the lock to be > something else than rwsem, but might_lock_read should still apply to > it and make sense ? I'm not sure what the extra API would bring... I guess at one time the API would become might_lock_read_a_range(), isn't it? Furthermore this would hiding the lock's name which the goal of this series.
On Tue, May 19, 2020 at 03:20:40PM +0200, Laurent Dufour wrote: > Le 19/05/2020 à 15:10, Michel Lespinasse a écrit : > > On Mon, May 18, 2020 at 03:45:22PM +0200, Laurent Dufour wrote: > > > Le 24/04/2020 à 03:39, Michel Lespinasse a écrit : > > > > Rename the mmap_sem field to mmap_lock. Any new uses of this lock > > > > should now go through the new mmap locking api. The mmap_lock is > > > > still implemented as a rwsem, though this could change in the future. > > > > > > > > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c > > > > index dc9ef302f517..701f3995f621 100644 > > > > --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c > > > > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c > > > > @@ -661,7 +661,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj) > > > > struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr; > > > > int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT; > > > > - might_lock_read(¤t->mm->mmap_sem); > > > > + might_lock_read(¤t->mm->mmap_lock); > > > > > > Why not a mm_might_lock_read() new API to hide the mmap_lock, and add it to > > > the previous patch? > > > > I'm not sure why this is needed - we may rework the lock to be > > something else than rwsem, but might_lock_read should still apply to > > it and make sense ? I'm not sure what the extra API would bring... > > I guess at one time the API would become might_lock_read_a_range(), isn't it? > Furthermore this would hiding the lock's name which the goal of this series. I think this assertion should be deleted from this driver. It's there in case get_user_pages_fast() takes the mmap sem. It would make sense to have this assertion in get_user_pages_fast() in case we take the fast path which doesn't acquire the mmap_sem. Something like this: +++ b/mm/gup.c @@ -2754,6 +2754,7 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, FOLL_FORCE | FOLL_PIN | FOLL_GET))) return -EINVAL; + might_lock_read(¤t->mm->mmap_lock); start = untagged_addr(start) & PAGE_MASK; addr = start; len = (unsigned long) nr_pages << PAGE_SHIFT;
On 2020-05-19 08:32, Matthew Wilcox wrote: > On Tue, May 19, 2020 at 03:20:40PM +0200, Laurent Dufour wrote: >> Le 19/05/2020 à 15:10, Michel Lespinasse a écrit : >>> On Mon, May 18, 2020 at 03:45:22PM +0200, Laurent Dufour wrote: >>>> Le 24/04/2020 à 03:39, Michel Lespinasse a écrit : >>>>> Rename the mmap_sem field to mmap_lock. Any new uses of this lock >>>>> should now go through the new mmap locking api. The mmap_lock is >>>>> still implemented as a rwsem, though this could change in the future. >>>>> >>>>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c >>>>> index dc9ef302f517..701f3995f621 100644 >>>>> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c >>>>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c >>>>> @@ -661,7 +661,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj) >>>>> struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr; >>>>> int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT; >>>>> - might_lock_read(¤t->mm->mmap_sem); >>>>> + might_lock_read(¤t->mm->mmap_lock); >>>> >>>> Why not a mm_might_lock_read() new API to hide the mmap_lock, and add it to >>>> the previous patch? >>> >>> I'm not sure why this is needed - we may rework the lock to be >>> something else than rwsem, but might_lock_read should still apply to >>> it and make sense ? I'm not sure what the extra API would bring... >> >> I guess at one time the API would become might_lock_read_a_range(), isn't it? >> Furthermore this would hiding the lock's name which the goal of this series. > > I think this assertion should be deleted from this driver. It's there > in case get_user_pages_fast() takes the mmap sem. It would make sense to > have this assertion in get_user_pages_fast() in case we take the fast path > which doesn't acquire the mmap_sem. Something like this: > > +++ b/mm/gup.c > @@ -2754,6 +2754,7 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, > FOLL_FORCE | FOLL_PIN | FOLL_GET))) > return -EINVAL; > > + might_lock_read(¤t->mm->mmap_lock); > start = untagged_addr(start) & PAGE_MASK; > addr = start; > len = (unsigned long) nr_pages << PAGE_SHIFT; > > Hi Michel and Matthew and all, There are a couple of recent developments in this code to keep in mind. I don't *think* either one is a problem here, but just in case: a) The latest version of the above routine [1] is on its way to mmotm as of yesterday, and that version more firmly divides the fast and slow parts, via a new FOLL_FAST_ONLY flag. The fall-back to slow/regular gup only occurs if the caller does not set FOLL_FAST_ONLY. (Note that it's a gup.c internal flag, btw.) That gives you additional options inside internal_get_user_pages_fast(), such as, approximately: if (!(gup_flags & FOLL_FAST_ONLY)) might_lock_read(¤t->mm->mmap_lock); ...not that that is necessarily a great idea, seeing as how it merely changes "might lock" into "maybe might lock". :) b) I've posted a small patch to that same etnaviv_gem.c file [2], over the weekend, to convert from get_user_pages()/put_page(), to pin_user_pages()/unpin_user_pages(). It hasn't been merged yet, and it shouldn't conflict either, but just one more reason to hope that the etnaviv list can do some run time testing on the whole lot. [1] https://lore.kernel.org/r/20200519002124.2025955-3-jhubbard@nvidia.com [2] https://lore.kernel.org/r/20200518054315.2407093-1-jhubbard@nvidia.com thanks,
On Tue, May 19, 2020 at 11:15 AM John Hubbard <jhubbard@nvidia.com> wrote: > On 2020-05-19 08:32, Matthew Wilcox wrote: > > On Tue, May 19, 2020 at 03:20:40PM +0200, Laurent Dufour wrote: > >> Le 19/05/2020 à 15:10, Michel Lespinasse a écrit : > >>> On Mon, May 18, 2020 at 03:45:22PM +0200, Laurent Dufour wrote: > >>>> Le 24/04/2020 à 03:39, Michel Lespinasse a écrit : > >>>>> Rename the mmap_sem field to mmap_lock. Any new uses of this lock > >>>>> should now go through the new mmap locking api. The mmap_lock is > >>>>> still implemented as a rwsem, though this could change in the future. > >>>>> > >>>>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c > >>>>> index dc9ef302f517..701f3995f621 100644 > >>>>> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c > >>>>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c > >>>>> @@ -661,7 +661,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj) > >>>>> struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr; > >>>>> int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT; > >>>>> - might_lock_read(¤t->mm->mmap_sem); > >>>>> + might_lock_read(¤t->mm->mmap_lock); > >>>> > >>>> Why not a mm_might_lock_read() new API to hide the mmap_lock, and add it to > >>>> the previous patch? > >>> > >>> I'm not sure why this is needed - we may rework the lock to be > >>> something else than rwsem, but might_lock_read should still apply to > >>> it and make sense ? I'm not sure what the extra API would bring... > >> > >> I guess at one time the API would become might_lock_read_a_range(), isn't it? I don't think this should be necessary - from lockdep perspective, there should not be a difference between locking a range vs the entire address space. > >> Furthermore this would hiding the lock's name which the goal of this series. Actually to me the name is very secondary - the goal of the series is to add an api abstracting the mmap locking. The lock name is secondary to that, it only gets renamed because mmap_sem was too specific (if we are to change the mmap locking) and to ensure we convert all direct uses to use the api instead. > > I think this assertion should be deleted from this driver. It's there > > in case get_user_pages_fast() takes the mmap sem. It would make sense to > > have this assertion in get_user_pages_fast() in case we take the fast path > > which doesn't acquire the mmap_sem. Something like this: I like this idea a lot - having might_lock assertions in get_user_pages_fast makes a log more sense than doing the same at the call sites. > There are a couple of recent developments in this code to keep in mind. I don't > *think* either one is a problem here, but just in case: > > a) The latest version of the above routine [1] is on its way to mmotm as of > yesterday, and that version more firmly divides the fast and slow parts, > via a new FOLL_FAST_ONLY flag. The fall-back to slow/regular gup only occurs > if the caller does not set FOLL_FAST_ONLY. (Note that it's a gup.c internal > flag, btw.) > > That gives you additional options inside internal_get_user_pages_fast(), such > as, approximately: > > if (!(gup_flags & FOLL_FAST_ONLY)) > might_lock_read(¤t->mm->mmap_lock); > > ...not that that is necessarily a great idea, seeing as how it merely changes > "might lock" into "maybe might lock". :) I think that is completely fine, makes sure everyone not using FOLL_FAST_ONLY realizes that the call could block. Can I ask you to add that assertion in your patchset ? Based on Matthew's feedback, I would do it in my patchset, but it doesn't seem worth doing if we know this will conflict with your changes.
On 2020-05-19 19:39, Michel Lespinasse wrote: ... >> That gives you additional options inside internal_get_user_pages_fast(), such >> as, approximately: >> >> if (!(gup_flags & FOLL_FAST_ONLY)) >> might_lock_read(¤t->mm->mmap_lock); >> >> ...not that that is necessarily a great idea, seeing as how it merely changes >> "might lock" into "maybe might lock". :) > > I think that is completely fine, makes sure everyone not using > FOLL_FAST_ONLY realizes that the call could block. > > Can I ask you to add that assertion in your patchset ? Based on > Matthew's feedback, I would do it in my patchset, but it doesn't seem > worth doing if we know this will conflict with your changes. > Sure, that's no problem. Although it looks like my changes may land in mmotm first, and then your patchset, so maybe the right move is to make this change *after* both of those things happen, yes? thanks,
On Wed, May 20, 2020 at 12:32 AM John Hubbard <jhubbard@nvidia.com> wrote: > On 2020-05-19 19:39, Michel Lespinasse wrote: > >> That gives you additional options inside internal_get_user_pages_fast(), such > >> as, approximately: > >> > >> if (!(gup_flags & FOLL_FAST_ONLY)) > >> might_lock_read(¤t->mm->mmap_lock); > >> > >> ...not that that is necessarily a great idea, seeing as how it merely changes > >> "might lock" into "maybe might lock". :) > > > > I think that is completely fine, makes sure everyone not using > > FOLL_FAST_ONLY realizes that the call could block. > > > > Can I ask you to add that assertion in your patchset ? Based on > > Matthew's feedback, I would do it in my patchset, but it doesn't seem > > worth doing if we know this will conflict with your changes. > > Sure, that's no problem. Although it looks like my changes may land > in mmotm first, and then your patchset, so maybe the right move is to > make this change *after* both of those things happen, yes? I don't have a strong opinion on this. I would suggest you add the might_lock_read() assertion and whoever comes in second will deal with the conflict by changing mmap_sem to mmap_lock in that assertion.
On Tue, May 19, 2020 at 07:39:30PM -0700, Michel Lespinasse wrote: > > > I think this assertion should be deleted from this driver. It's there > > > in case get_user_pages_fast() takes the mmap sem. It would make sense to > > > have this assertion in get_user_pages_fast() in case we take the fast path > > > which doesn't acquire the mmap_sem. Something like this: > > I like this idea a lot - having might_lock assertions in > get_user_pages_fast makes a log more sense than doing the same at the > call sites. +1 I've wanted to see more complete lockdep annotations in gup.c for a while now.. There has been a number of bugs this would have caught Jason
diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c index 693f00b117e1..9b95050c2048 100644 --- a/arch/ia64/mm/fault.c +++ b/arch/ia64/mm/fault.c @@ -70,8 +70,8 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re mask = ((((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT) | (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT)); - /* mmap_sem is performance critical.... */ - prefetchw(&mm->mmap_sem); + /* mmap_lock is performance critical.... */ + prefetchw(&mm->mmap_lock); /* * If we're in an interrupt or have no user context, we must not take the fault.. diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 181f66b9049f..35f530f9dfc0 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1522,7 +1522,7 @@ dotraplinkage void do_page_fault(struct pt_regs *regs, unsigned long hw_error_code, unsigned long address) { - prefetchw(¤t->mm->mmap_sem); + prefetchw(¤t->mm->mmap_lock); trace_page_fault_entries(regs, hw_error_code, address); if (unlikely(kmmio_fault(regs, address))) diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c index dc9ef302f517..701f3995f621 100644 --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c @@ -661,7 +661,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj) struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr; int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT; - might_lock_read(¤t->mm->mmap_sem); + might_lock_read(¤t->mm->mmap_lock); if (userptr->mm != current->mm) return -EPERM; diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 4aba6c0c2ba8..d13b90399c16 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -436,7 +436,7 @@ struct mm_struct { spinlock_t page_table_lock; /* Protects page tables and some * counters */ - struct rw_semaphore mmap_sem; + struct rw_semaphore mmap_lock; struct list_head mmlist; /* List of maybe swapped mm's. These * are globally strung together off diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index 5bf7cee5d93b..9dc632add390 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -4,67 +4,67 @@ #include <linux/mmdebug.h> #define MMAP_LOCK_INITIALIZER(name) \ - .mmap_sem = __RWSEM_INITIALIZER(name.mmap_sem), + .mmap_lock = __RWSEM_INITIALIZER(name.mmap_lock), static inline void mmap_init_lock(struct mm_struct *mm) { - init_rwsem(&mm->mmap_sem); + init_rwsem(&mm->mmap_lock); } static inline void mmap_write_lock(struct mm_struct *mm) { - down_write(&mm->mmap_sem); + down_write(&mm->mmap_lock); } static inline void mmap_write_lock_nested(struct mm_struct *mm, int subclass) { - down_write_nested(&mm->mmap_sem, subclass); + down_write_nested(&mm->mmap_lock, subclass); } static inline int mmap_write_lock_killable(struct mm_struct *mm) { - return down_write_killable(&mm->mmap_sem); + return down_write_killable(&mm->mmap_lock); } static inline bool mmap_write_trylock(struct mm_struct *mm) { - return down_write_trylock(&mm->mmap_sem) != 0; + return down_write_trylock(&mm->mmap_lock) != 0; } static inline void mmap_write_unlock(struct mm_struct *mm) { - up_write(&mm->mmap_sem); + up_write(&mm->mmap_lock); } static inline void mmap_write_downgrade(struct mm_struct *mm) { - downgrade_write(&mm->mmap_sem); + downgrade_write(&mm->mmap_lock); } static inline void mmap_read_lock(struct mm_struct *mm) { - down_read(&mm->mmap_sem); + down_read(&mm->mmap_lock); } static inline int mmap_read_lock_killable(struct mm_struct *mm) { - return down_read_killable(&mm->mmap_sem); + return down_read_killable(&mm->mmap_lock); } static inline bool mmap_read_trylock(struct mm_struct *mm) { - return down_read_trylock(&mm->mmap_sem) != 0; + return down_read_trylock(&mm->mmap_lock) != 0; } static inline void mmap_read_unlock(struct mm_struct *mm) { - up_read(&mm->mmap_sem); + up_read(&mm->mmap_lock); } static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm) { - if (down_read_trylock(&mm->mmap_sem)) { - rwsem_release(&mm->mmap_sem.dep_map, _RET_IP_); + if (down_read_trylock(&mm->mmap_lock)) { + rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_); return true; } return false; @@ -72,19 +72,19 @@ static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm) static inline void mmap_read_unlock_non_owner(struct mm_struct *mm) { - up_read_non_owner(&mm->mmap_sem); + up_read_non_owner(&mm->mmap_lock); } static inline void mmap_assert_locked(struct mm_struct *mm) { - VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_sem, -1), mm); - VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm); + VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_lock, -1), mm); + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); } static inline void mmap_assert_write_locked(struct mm_struct *mm) { - VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_sem, 0), mm); - VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm); + VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_lock, 0), mm); + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); } #endif /* _LINUX_MMAP_LOCK_H */ diff --git a/mm/memory.c b/mm/memory.c index 20f98ea8968e..c2963e7affa9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4811,7 +4811,7 @@ void __might_fault(const char *file, int line) __might_sleep(file, line, 0); #if defined(CONFIG_DEBUG_ATOMIC_SLEEP) if (current->mm) - might_lock_read(¤t->mm->mmap_sem); + might_lock_read(¤t->mm->mmap_lock); #endif } EXPORT_SYMBOL(__might_fault); diff --git a/mm/mmap.c b/mm/mmap.c index 2f4ffccc5972..80a47031d5db 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3474,7 +3474,7 @@ static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma) * The LSB of head.next can't change from under us * because we hold the mm_all_locks_mutex. */ - down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_sem); + down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_lock); /* * We can safely modify head.next after taking the * anon_vma->root->rwsem. If some other vma in this mm shares @@ -3504,7 +3504,7 @@ static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping) */ if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags)) BUG(); - down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_sem); + down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_lock); } } diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c index 24eb9d1ed0a7..2f348b6c9c9a 100644 --- a/mm/mmu_notifier.c +++ b/mm/mmu_notifier.c @@ -983,7 +983,7 @@ int mmu_interval_notifier_insert(struct mmu_interval_notifier *interval_sub, struct mmu_notifier_subscriptions *subscriptions; int ret; - might_lock(&mm->mmap_sem); + might_lock(&mm->mmap_lock); subscriptions = smp_load_acquire(&mm->notifier_subscriptions); if (!subscriptions || !subscriptions->has_itree) {
Rename the mmap_sem field to mmap_lock. Any new uses of this lock should now go through the new mmap locking api. The mmap_lock is still implemented as a rwsem, though this could change in the future. Signed-off-by: Michel Lespinasse <walken@google.com> --- arch/ia64/mm/fault.c | 4 +-- arch/x86/mm/fault.c | 2 +- drivers/gpu/drm/etnaviv/etnaviv_gem.c | 2 +- include/linux/mm_types.h | 2 +- include/linux/mmap_lock.h | 38 +++++++++++++-------------- mm/memory.c | 2 +- mm/mmap.c | 4 +-- mm/mmu_notifier.c | 2 +- 8 files changed, 28 insertions(+), 28 deletions(-)