Messages in this thread Patch in this message | | | Date | Wed, 10 Jun 2009 11:10:00 +0800 | From | Wu Fengguang <> | Subject | [PATCH] HWPOISON: fix tasklist_lock/anon_vma locking order |
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On Tue, Jun 09, 2009 at 06:09:22PM +0800, Nick Piggin wrote: > On Wed, Jun 03, 2009 at 08:46:47PM +0200, Andi Kleen wrote: > > Why not have this in rmap.c and not export the locking? > I don't know.. does Hugh care?
I don't know either :)
> > +/* > > + * Collect processes when the error hit an anonymous page. > > + */ > > +static void collect_procs_anon(struct page *page, struct list_head *to_kill, > > + struct to_kill **tkc) > > +{ > > + struct vm_area_struct *vma; > > + struct task_struct *tsk; > > + struct anon_vma *av = page_lock_anon_vma(page); > > + > > + if (av == NULL) /* Not actually mapped anymore */ > > + return; > > + > > + read_lock(&tasklist_lock); > > + for_each_process (tsk) { > > + if (!tsk->mm) > > + continue; > > + list_for_each_entry (vma, &av->head, anon_vma_node) { > > + if (vma->vm_mm == tsk->mm) > > + add_to_kill(tsk, page, vma, to_kill, tkc); > > + } > > + } > > + page_unlock_anon_vma(av); > > + read_unlock(&tasklist_lock); > > +} > > + > > +/* > > + * Collect processes when the error hit a file mapped page. > > + */ > > +static void collect_procs_file(struct page *page, struct list_head *to_kill, > > + struct to_kill **tkc) > > +{ > > + struct vm_area_struct *vma; > > + struct task_struct *tsk; > > + struct prio_tree_iter iter; > > + struct address_space *mapping = page_mapping(page); > > + > > + /* > > + * A note on the locking order between the two locks. > > + * We don't rely on this particular order. > > + * If you have some other code that needs a different order > > + * feel free to switch them around. Or add a reverse link > > + * from mm_struct to task_struct, then this could be all > > + * done without taking tasklist_lock and looping over all tasks. > > + */ > > + > > + read_lock(&tasklist_lock); > > + spin_lock(&mapping->i_mmap_lock); > > This still has my original complaint that it nests tasklist lock inside > anon vma lock and outside inode mmap lock (and anon_vma nests inside i_mmap). > I guess the property of our current rw locks means that does not matter, > but it could if we had "fair" rw locks, or some tree (-rt tree maybe) > changed rw lock to a plain exclusive lock.
Andi must forgot that - he did change the comment on locking order. This incremental patch aligns the code with his comment in rmap.c.
--- HWPOISON: fix tasklist_lock/anon_vma locking order
To avoid possible deadlock. Proposed by Nick Piggin:
You have tasklist_lock(R) nesting outside i_mmap_lock, and inside anon_vma lock. And anon_vma lock nests inside i_mmap_lock.
This seems fragile. If rwlocks ever become FIFO or tasklist_lock changes type (maybe -rt kernels do it), then you could have a task holding anon_vma lock and waiting for tasklist_lock, and another holding tasklist lock and waiting for i_mmap_lock, and another holding i_mmap_lock and waiting for anon_vma lock.
CC: Nick Piggin <npiggin@suse.de> CC: Andi Kleen <andi@firstfloor.org> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com> --- mm/memory-failure.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
--- sound-2.6.orig/mm/memory-failure.c +++ sound-2.6/mm/memory-failure.c @@ -215,12 +215,14 @@ static void collect_procs_anon(struct pa { struct vm_area_struct *vma; struct task_struct *tsk; - struct anon_vma *av = page_lock_anon_vma(page); + struct anon_vma *av; + read_lock(&tasklist_lock); + + av = page_lock_anon_vma(page); if (av == NULL) /* Not actually mapped anymore */ - return; + goto out; - read_lock(&tasklist_lock); for_each_process (tsk) { if (!tsk->mm) continue; @@ -230,6 +232,7 @@ static void collect_procs_anon(struct pa } } page_unlock_anon_vma(av); +out: read_unlock(&tasklist_lock); }
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