| Message ID | 1474992504-20133-20-git-send-email-jack@suse.cz (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
On Tue, Sep 27, 2016 at 06:08:23PM +0200, Jan Kara wrote: > Currently PTE gets updated in wp_pfn_shared() after dax_pfn_mkwrite() > has released corresponding radix tree entry lock. When we want to > writeprotect PTE on cache flush, we need PTE modification to happen > under radix tree entry lock to ensure consisten updates of PTE and radix consistent > tree (standard faults use page lock to ensure this consistency). So move > update of PTE bit into dax_pfn_mkwrite(). > > Signed-off-by: Jan Kara <jack@suse.cz> > --- > fs/dax.c | 22 ++++++++++++++++------ > mm/memory.c | 2 +- > 2 files changed, 17 insertions(+), 7 deletions(-) > > diff --git a/fs/dax.c b/fs/dax.c > index c6cadf8413a3..a2d3781c9f4e 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -1163,17 +1163,27 @@ int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) > { > struct file *file = vma->vm_file; > struct address_space *mapping = file->f_mapping; > - void *entry; > + void *entry, **slot; > pgoff_t index = vmf->pgoff; > > spin_lock_irq(&mapping->tree_lock); > - entry = get_unlocked_mapping_entry(mapping, index, NULL); > - if (!entry || !radix_tree_exceptional_entry(entry)) > - goto out; > + entry = get_unlocked_mapping_entry(mapping, index, &slot); > + if (!entry || !radix_tree_exceptional_entry(entry)) { > + if (entry) > + put_unlocked_mapping_entry(mapping, index, entry); I don't think you need this call to put_unlocked_mapping_entry(). If we get in here we know that 'entry' is a page cache page, in which case put_unlocked_mapping_entry() will just return without doing any work. With that nit & the spelling error above: Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
On Tue 18-10-16 13:53:32, Ross Zwisler wrote: > On Tue, Sep 27, 2016 at 06:08:23PM +0200, Jan Kara wrote: > > - void *entry; > > + void *entry, **slot; > > pgoff_t index = vmf->pgoff; > > > > spin_lock_irq(&mapping->tree_lock); > > - entry = get_unlocked_mapping_entry(mapping, index, NULL); > > - if (!entry || !radix_tree_exceptional_entry(entry)) > > - goto out; > > + entry = get_unlocked_mapping_entry(mapping, index, &slot); > > + if (!entry || !radix_tree_exceptional_entry(entry)) { > > + if (entry) > > + put_unlocked_mapping_entry(mapping, index, entry); > > I don't think you need this call to put_unlocked_mapping_entry(). If we get > in here we know that 'entry' is a page cache page, in which case > put_unlocked_mapping_entry() will just return without doing any work. Right, but that is just an implementation detail internal to how the locking works. The rules are simple to avoid issues and thus the invariant is: Once you call get_unlocked_mapping_entry() you either have to lock the entry and then call put_locked_mapping_entry() or you have to drop it with put_unlocked_mapping_entry(). Once you add arguments about entry types etc., errors are much easier to make... Honza
On Wed, Oct 19, 2016 at 09:25:05AM +0200, Jan Kara wrote: > On Tue 18-10-16 13:53:32, Ross Zwisler wrote: > > On Tue, Sep 27, 2016 at 06:08:23PM +0200, Jan Kara wrote: > > > - void *entry; > > > + void *entry, **slot; > > > pgoff_t index = vmf->pgoff; > > > > > > spin_lock_irq(&mapping->tree_lock); > > > - entry = get_unlocked_mapping_entry(mapping, index, NULL); > > > - if (!entry || !radix_tree_exceptional_entry(entry)) > > > - goto out; > > > + entry = get_unlocked_mapping_entry(mapping, index, &slot); > > > + if (!entry || !radix_tree_exceptional_entry(entry)) { > > > + if (entry) > > > + put_unlocked_mapping_entry(mapping, index, entry); > > > > I don't think you need this call to put_unlocked_mapping_entry(). If we get > > in here we know that 'entry' is a page cache page, in which case > > put_unlocked_mapping_entry() will just return without doing any work. > > Right, but that is just an implementation detail internal to how the > locking works. The rules are simple to avoid issues and thus the invariant > is: Once you call get_unlocked_mapping_entry() you either have to lock the > entry and then call put_locked_mapping_entry() or you have to drop it with > put_unlocked_mapping_entry(). Once you add arguments about entry types > etc., errors are much easier to make... Makes sense. You can add: Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
diff --git a/fs/dax.c b/fs/dax.c index c6cadf8413a3..a2d3781c9f4e 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1163,17 +1163,27 @@ int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) { struct file *file = vma->vm_file; struct address_space *mapping = file->f_mapping; - void *entry; + void *entry, **slot; pgoff_t index = vmf->pgoff; spin_lock_irq(&mapping->tree_lock); - entry = get_unlocked_mapping_entry(mapping, index, NULL); - if (!entry || !radix_tree_exceptional_entry(entry)) - goto out; + entry = get_unlocked_mapping_entry(mapping, index, &slot); + if (!entry || !radix_tree_exceptional_entry(entry)) { + if (entry) + put_unlocked_mapping_entry(mapping, index, entry); + spin_unlock_irq(&mapping->tree_lock); + return VM_FAULT_NOPAGE; + } radix_tree_tag_set(&mapping->page_tree, index, PAGECACHE_TAG_DIRTY); - put_unlocked_mapping_entry(mapping, index, entry); -out: + entry = lock_slot(mapping, slot); spin_unlock_irq(&mapping->tree_lock); + /* + * If we race with somebody updating the PTE and finish_mkwrite_fault() + * fails, we don't care. We need to return VM_FAULT_NOPAGE and retry + * the fault in either case. + */ + finish_mkwrite_fault(vmf); + put_locked_mapping_entry(mapping, index, entry); return VM_FAULT_NOPAGE; } EXPORT_SYMBOL_GPL(dax_pfn_mkwrite); diff --git a/mm/memory.c b/mm/memory.c index e7a4a30a5e88..5fa3d0c5196e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2310,7 +2310,7 @@ static int wp_pfn_shared(struct vm_fault *vmf) pte_unmap_unlock(vmf->pte, vmf->ptl); vmf->flags |= FAULT_FLAG_MKWRITE; ret = vma->vm_ops->pfn_mkwrite(vma, vmf); - if (ret & VM_FAULT_ERROR) + if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)) return ret; return finish_mkwrite_fault(vmf); }
Currently PTE gets updated in wp_pfn_shared() after dax_pfn_mkwrite() has released corresponding radix tree entry lock. When we want to writeprotect PTE on cache flush, we need PTE modification to happen under radix tree entry lock to ensure consisten updates of PTE and radix tree (standard faults use page lock to ensure this consistency). So move update of PTE bit into dax_pfn_mkwrite(). Signed-off-by: Jan Kara <jack@suse.cz> --- fs/dax.c | 22 ++++++++++++++++------ mm/memory.c | 2 +- 2 files changed, 17 insertions(+), 7 deletions(-)