| Message ID | 1444170529-12814-2-git-send-email-ross.zwisler@linux.intel.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
On Tue, Oct 6, 2015 at 3:28 PM, Ross Zwisler <ross.zwisler@linux.intel.com> wrote: > This reverts commits 46c043ede4711e8d598b9d63c5616c1fedb0605e > and 8346c416d17bf5b4ea1508662959bb62e73fd6a5. > > The following two locking commits in the DAX code: > > commit 843172978bb9 ("dax: fix race between simultaneous faults") > commit 46c043ede471 ("mm: take i_mmap_lock in unmap_mapping_range() for DAX") > > introduced a number of deadlocks and other issues, and need to be > reverted for the v4.3 kernel. The list of issues in DAX after these > commits (some newly introduced by the commits, some preexisting) can be > found here: > > https://lkml.org/lkml/2015/9/25/602 > > This revert keeps the PMEM API changes to the zeroing code in > __dax_pmd_fault(), which were added by this commit: > > commit d77e92e270ed ("dax: update PMD fault handler with PMEM API") > > It also keeps the code dropping mapping->i_mmap_rwsem before calling > unmap_mapping_range(), but converts it to a read lock since that's what is > now used by the rest of __dax_pmd_fault(). This is needed to avoid > recursively acquiring mapping->i_mmap_rwsem, once with a read lock in > __dax_pmd_fault() and once with a write lock in unmap_mapping_range(). I think it is safe to say that this has now morphed into a full blown fix and the "revert" label no longer applies. But, I'll let Andrew weigh in if he wants that fixed up or will replace these patches in -mm: revert-mm-take-i_mmap_lock-in-unmap_mapping_range-for-dax.patch revert-dax-fix-race-between-simultaneous-faults.patch dax-temporarily-disable-dax-pmd-fault-path.patch ...with this new series. However, a question below: > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> > --- > fs/dax.c | 37 +++++++++++++------------------------ > mm/memory.c | 11 +++++++++-- > 2 files changed, 22 insertions(+), 26 deletions(-) > > diff --git a/fs/dax.c b/fs/dax.c > index bcfb14b..f665bc9 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -569,36 +569,14 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, > if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) > goto fallback; > > - sector = bh.b_blocknr << (blkbits - 9); > - > - if (buffer_unwritten(&bh) || buffer_new(&bh)) { > - int i; > - > - length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn, > - bh.b_size); > - if (length < 0) { > - result = VM_FAULT_SIGBUS; > - goto out; > - } > - if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR)) > - goto fallback; > - > - for (i = 0; i < PTRS_PER_PMD; i++) > - clear_pmem(kaddr + i * PAGE_SIZE, PAGE_SIZE); > - wmb_pmem(); > - count_vm_event(PGMAJFAULT); > - mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT); > - result |= VM_FAULT_MAJOR; > - } > - > /* > * If we allocated new storage, make sure no process has any > * zero pages covering this hole > */ > if (buffer_new(&bh)) { > - i_mmap_unlock_write(mapping); > + i_mmap_unlock_read(mapping); > unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0); > - i_mmap_lock_write(mapping); > + i_mmap_lock_read(mapping); > } > > /* > @@ -635,6 +613,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, > result = VM_FAULT_NOPAGE; > spin_unlock(ptl); > } else { > + sector = bh.b_blocknr << (blkbits - 9); > length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn, > bh.b_size); > if (length < 0) { > @@ -644,6 +623,16 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, > if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR)) > goto fallback; > > + if (buffer_unwritten(&bh) || buffer_new(&bh)) { > + int i; > + for (i = 0; i < PTRS_PER_PMD; i++) > + clear_pmem(kaddr + i * PAGE_SIZE, PAGE_SIZE); > + wmb_pmem(); > + count_vm_event(PGMAJFAULT); > + mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT); > + result |= VM_FAULT_MAJOR; > + } > + > result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write); > } > > diff --git a/mm/memory.c b/mm/memory.c > index 9cb2747..5ec066f 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2426,10 +2426,17 @@ void unmap_mapping_range(struct address_space *mapping, > if (details.last_index < details.first_index) > details.last_index = ULONG_MAX; > > - i_mmap_lock_write(mapping); > + > + /* > + * DAX already holds i_mmap_lock to serialise file truncate vs > + * page fault and page fault vs page fault. > + */ > + if (!IS_DAX(mapping->host)) > + i_mmap_lock_write(mapping); > if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap))) > unmap_mapping_range_tree(&mapping->i_mmap, &details); > - i_mmap_unlock_write(mapping); > + if (!IS_DAX(mapping->host)) > + i_mmap_unlock_write(mapping); > } > EXPORT_SYMBOL(unmap_mapping_range); What about cases where unmap_mapping_range() is called without an fs lock? For the get_user_pages() and ZONE_DEVICE implementation I'm looking to call truncate_pagecache() from the driver shutdown path to revoke usage of the struct page's that were allocated by devm_memremap_pages(). Likely I'm introducing a path through unmap_mapping_range() that does not exist today, but I don't like that unmap_mapping_range() with this change is presuming a given locking context. It's not clear to me how this routine is safe when it optionally takes i_mmap_lock_write(), at a minimum this needs documenting, and possibly assertions if the locking assumptions are violated. invalidate_inode_pages2_range() seems to call unmap_mapping_range() without the the correct locking, but this was just a quick scan.
On Wed, Oct 07, 2015 at 09:19:28AM -0700, Dan Williams wrote: > On Tue, Oct 6, 2015 at 3:28 PM, Ross Zwisler > <ross.zwisler@linux.intel.com> wrote: <snip> > > diff --git a/mm/memory.c b/mm/memory.c > > index 9cb2747..5ec066f 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -2426,10 +2426,17 @@ void unmap_mapping_range(struct address_space *mapping, > > if (details.last_index < details.first_index) > > details.last_index = ULONG_MAX; > > > > - i_mmap_lock_write(mapping); > > + > > + /* > > + * DAX already holds i_mmap_lock to serialise file truncate vs > > + * page fault and page fault vs page fault. > > + */ > > + if (!IS_DAX(mapping->host)) > > + i_mmap_lock_write(mapping); > > if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap))) > > unmap_mapping_range_tree(&mapping->i_mmap, &details); > > - i_mmap_unlock_write(mapping); > > + if (!IS_DAX(mapping->host)) > > + i_mmap_unlock_write(mapping); > > } > > EXPORT_SYMBOL(unmap_mapping_range); > > What about cases where unmap_mapping_range() is called without an fs > lock? For the get_user_pages() and ZONE_DEVICE implementation I'm > looking to call truncate_pagecache() from the driver shutdown path to > revoke usage of the struct page's that were allocated by > devm_memremap_pages(). > > Likely I'm introducing a path through unmap_mapping_range() that does > not exist today, but I don't like that unmap_mapping_range() with this > change is presuming a given locking context. It's not clear to me how > this routine is safe when it optionally takes i_mmap_lock_write(), at > a minimum this needs documenting, and possibly assertions if the > locking assumptions are violated. Yep, this is very confusing - these changes were undone by the second revert in the series (they were done and then undone by separate patches, both of which are getting reverted). After the series is applied in total unmap_mapping_range() takes the locks unconditionally: /* DAX uses i_mmap_lock to serialise file truncate vs page fault */ i_mmap_lock_write(mapping); if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap))) unmap_mapping_range_tree(&mapping->i_mmap, &details); i_mmap_unlock_write(mapping); } EXPORT_SYMBOL(unmap_mapping_range); Yes, I totally agree this is confusing - I'll just bit the bullet, collapse the two reverts together and call it "dax locking fixes" or something.
diff --git a/fs/dax.c b/fs/dax.c index bcfb14b..f665bc9 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -569,36 +569,14 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) goto fallback; - sector = bh.b_blocknr << (blkbits - 9); - - if (buffer_unwritten(&bh) || buffer_new(&bh)) { - int i; - - length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn, - bh.b_size); - if (length < 0) { - result = VM_FAULT_SIGBUS; - goto out; - } - if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR)) - goto fallback; - - for (i = 0; i < PTRS_PER_PMD; i++) - clear_pmem(kaddr + i * PAGE_SIZE, PAGE_SIZE); - wmb_pmem(); - count_vm_event(PGMAJFAULT); - mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT); - result |= VM_FAULT_MAJOR; - } - /* * If we allocated new storage, make sure no process has any * zero pages covering this hole */ if (buffer_new(&bh)) { - i_mmap_unlock_write(mapping); + i_mmap_unlock_read(mapping); unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0); - i_mmap_lock_write(mapping); + i_mmap_lock_read(mapping); } /* @@ -635,6 +613,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, result = VM_FAULT_NOPAGE; spin_unlock(ptl); } else { + sector = bh.b_blocknr << (blkbits - 9); length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn, bh.b_size); if (length < 0) { @@ -644,6 +623,16 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR)) goto fallback; + if (buffer_unwritten(&bh) || buffer_new(&bh)) { + int i; + for (i = 0; i < PTRS_PER_PMD; i++) + clear_pmem(kaddr + i * PAGE_SIZE, PAGE_SIZE); + wmb_pmem(); + count_vm_event(PGMAJFAULT); + mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT); + result |= VM_FAULT_MAJOR; + } + result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write); } diff --git a/mm/memory.c b/mm/memory.c index 9cb2747..5ec066f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2426,10 +2426,17 @@ void unmap_mapping_range(struct address_space *mapping, if (details.last_index < details.first_index) details.last_index = ULONG_MAX; - i_mmap_lock_write(mapping); + + /* + * DAX already holds i_mmap_lock to serialise file truncate vs + * page fault and page fault vs page fault. + */ + if (!IS_DAX(mapping->host)) + i_mmap_lock_write(mapping); if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap))) unmap_mapping_range_tree(&mapping->i_mmap, &details); - i_mmap_unlock_write(mapping); + if (!IS_DAX(mapping->host)) + i_mmap_unlock_write(mapping); } EXPORT_SYMBOL(unmap_mapping_range);
This reverts commits 46c043ede4711e8d598b9d63c5616c1fedb0605e and 8346c416d17bf5b4ea1508662959bb62e73fd6a5. The following two locking commits in the DAX code: commit 843172978bb9 ("dax: fix race between simultaneous faults") commit 46c043ede471 ("mm: take i_mmap_lock in unmap_mapping_range() for DAX") introduced a number of deadlocks and other issues, and need to be reverted for the v4.3 kernel. The list of issues in DAX after these commits (some newly introduced by the commits, some preexisting) can be found here: https://lkml.org/lkml/2015/9/25/602 This revert keeps the PMEM API changes to the zeroing code in __dax_pmd_fault(), which were added by this commit: commit d77e92e270ed ("dax: update PMD fault handler with PMEM API") It also keeps the code dropping mapping->i_mmap_rwsem before calling unmap_mapping_range(), but converts it to a read lock since that's what is now used by the rest of __dax_pmd_fault(). This is needed to avoid recursively acquiring mapping->i_mmap_rwsem, once with a read lock in __dax_pmd_fault() and once with a write lock in unmap_mapping_range(). Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> --- fs/dax.c | 37 +++++++++++++------------------------ mm/memory.c | 11 +++++++++-- 2 files changed, 22 insertions(+), 26 deletions(-)