Re: [patch for-3.7] mm, mempolicy: fix printing stack contents innuma_maps
From: David Rientjes
Date: Wed Oct 17 2012 - 01:24:26 EST
On Wed, 17 Oct 2012, Dave Jones wrote:
> BUG: sleeping function called from invalid context at kernel/mutex.c:269
> in_atomic(): 1, irqs_disabled(): 0, pid: 8558, name: trinity-child2
> 3 locks on stack by trinity-child2/8558:
> #0: held: (&p->lock){+.+.+.}, instance: ffff88010c9a00b0, at: [<ffffffff8120cd1f>] seq_lseek+0x3f/0x120
> #1: held: (&mm->mmap_sem){++++++}, instance: ffff88013956f7c8, at: [<ffffffff81254437>] m_start+0xa7/0x190
> #2: held: (&(&p->alloc_lock)->rlock){+.+...}, instance: ffff88011fc64f30, at: [<ffffffff81254f8f>] show_numa_map+0x14f/0x610
> Pid: 8558, comm: trinity-child2 Not tainted 3.7.0-rc1+ #32
> Call Trace:
> [<ffffffff810ae4ec>] __might_sleep+0x14c/0x200
> [<ffffffff816bdf4e>] mutex_lock_nested+0x2e/0x50
> [<ffffffff811c43a3>] mpol_shared_policy_lookup+0x33/0x90
> [<ffffffff8118d5c3>] shmem_get_policy+0x33/0x40
> [<ffffffff811c31fa>] get_vma_policy+0x3a/0x90
> [<ffffffff81254fa3>] show_numa_map+0x163/0x610
> [<ffffffff81255b10>] ? pid_maps_open+0x20/0x20
> [<ffffffff81255980>] ? pagemap_hugetlb_range+0xf0/0xf0
> [<ffffffff81255483>] show_pid_numa_map+0x13/0x20
> [<ffffffff8120c902>] traverse+0xf2/0x230
> [<ffffffff8120cd8b>] seq_lseek+0xab/0x120
> [<ffffffff811e6c0b>] sys_lseek+0x7b/0xb0
> [<ffffffff816ca088>] tracesys+0xe1/0xe6
>
Hmm, looks like we need to change the refcount semantics entirely. We'll
need to make get_vma_policy() always take a reference and then drop it
accordingly. This work sif get_vma_policy() can grab a reference while
holding task_lock() for the task policy fallback case.
Comments on this approach?
---
fs/proc/task_mmu.c | 4 +---
include/linux/mm.h | 3 +--
mm/hugetlb.c | 4 ++--
mm/mempolicy.c | 41 ++++++++++++++++++++++-------------------
4 files changed, 26 insertions(+), 26 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1178,11 +1178,9 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
walk.private = md;
walk.mm = mm;
- task_lock(task);
pol = get_vma_policy(task, vma, vma->vm_start);
mpol_to_str(buffer, sizeof(buffer), pol, 0);
- mpol_cond_put(pol);
- task_unlock(task);
+ __mpol_put(pol);
seq_printf(m, "%08lx %s", vma->vm_start, buffer);
diff --git a/include/linux/mm.h b/include/linux/mm.h
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -216,8 +216,7 @@ struct vm_operations_struct {
* get_policy() op must add reference [mpol_get()] to any policy at
* (vma,addr) marked as MPOL_SHARED. The shared policy infrastructure
* in mm/mempolicy.c will do this automatically.
- * get_policy() must NOT add a ref if the policy at (vma,addr) is not
- * marked as MPOL_SHARED. vma policies are protected by the mmap_sem.
+ * vma policies are protected by the mmap_sem.
* If no [shared/vma] mempolicy exists at the addr, get_policy() op
* must return NULL--i.e., do not "fallback" to task or system default
* policy.
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -568,13 +568,13 @@ retry_cpuset:
}
}
- mpol_cond_put(mpol);
+ __mpol_put(mpol);
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
goto retry_cpuset;
return page;
err:
- mpol_cond_put(mpol);
+ __mpol_put(mpol);
return NULL;
}
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1536,39 +1536,41 @@ asmlinkage long compat_sys_mbind(compat_ulong_t start, compat_ulong_t len,
*
* Returns effective policy for a VMA at specified address.
* Falls back to @task or system default policy, as necessary.
- * Current or other task's task mempolicy and non-shared vma policies must be
- * protected by task_lock(task) by the caller.
- * Shared policies [those marked as MPOL_F_SHARED] require an extra reference
- * count--added by the get_policy() vm_op, as appropriate--to protect against
- * freeing by another task. It is the caller's responsibility to free the
- * extra reference for shared policies.
+ * Increments the reference count of the returned mempolicy, it is the caller's
+ * responsibility to decrement with __mpol_put().
+ * Requires vma->vm_mm->mmap_sem to be held for vma policies and takes
+ * task_lock(task) for task policy fallback.
*/
struct mempolicy *get_vma_policy(struct task_struct *task,
struct vm_area_struct *vma, unsigned long addr)
{
- struct mempolicy *pol = task->mempolicy;
+ struct mempolicy *pol;
+
+ task_lock(task);
+ pol = task->mempolicy;
+ mpol_get(pol);
+ task_unlock(task);
if (vma) {
if (vma->vm_ops && vma->vm_ops->get_policy) {
struct mempolicy *vpol = vma->vm_ops->get_policy(vma,
addr);
- if (vpol)
+ if (vpol) {
+ mpol_put(pol);
pol = vpol;
+ if (!mpol_needs_cond_ref(pol))
+ mpol_get(pol);
+ }
} else if (vma->vm_policy) {
+ mpol_put(pol);
pol = vma->vm_policy;
-
- /*
- * shmem_alloc_page() passes MPOL_F_SHARED policy with
- * a pseudo vma whose vma->vm_ops=NULL. Take a reference
- * count on these policies which will be dropped by
- * mpol_cond_put() later
- */
- if (mpol_needs_cond_ref(pol))
- mpol_get(pol);
+ mpol_get(pol);
}
}
- if (!pol)
+ if (!pol) {
pol = &default_policy;
+ mpol_get(pol);
+ }
return pol;
}
@@ -1919,7 +1921,7 @@ retry_cpuset:
unsigned nid;
nid = interleave_nid(pol, vma, addr, PAGE_SHIFT + order);
- mpol_cond_put(pol);
+ __mpol_put(pol);
page = alloc_page_interleave(gfp, order, nid);
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
goto retry_cpuset;
@@ -1943,6 +1945,7 @@ retry_cpuset:
*/
page = __alloc_pages_nodemask(gfp, order, zl,
policy_nodemask(gfp, pol));
+ __mpol_put(pol);
if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
goto retry_cpuset;
return page;
--
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