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author | KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> | 2012-10-19 10:00:55 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-10-19 23:32:10 +0200 |
commit | 9e7814404b77c3e8920bee4277162bf3a7460505 (patch) | |
tree | f7542b049f29150680507dd211925401beadac9a /fs/proc/task_mmu.c | |
parent | Merge branch 'x86/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/ti... (diff) | |
download | linux-9e7814404b77c3e8920bee4277162bf3a7460505.tar.xz linux-9e7814404b77c3e8920bee4277162bf3a7460505.zip |
hold task->mempolicy while numa_maps scans.
/proc/<pid>/numa_maps scans vma and show mempolicy under
mmap_sem. It sometimes accesses task->mempolicy which can
be freed without mmap_sem and numa_maps can show some
garbage while scanning.
This patch tries to take reference count of task->mempolicy at reading
numa_maps before calling get_vma_policy(). By this, task->mempolicy
will not be freed until numa_maps reaches its end.
V2->v3
- updated comments to be more verbose.
- removed task_lock() in numa_maps code.
V1->V2
- access task->mempolicy only once and remember it. Becase kernel/exit.c
can overwrite it.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/proc/task_mmu.c')
-rw-r--r-- | fs/proc/task_mmu.c | 50 |
1 files changed, 47 insertions, 3 deletions
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 14df8806ff29..90c63f9392a5 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -90,10 +90,55 @@ static void pad_len_spaces(struct seq_file *m, int len) seq_printf(m, "%*c", len, ' '); } +#ifdef CONFIG_NUMA +/* + * These functions are for numa_maps but called in generic **maps seq_file + * ->start(), ->stop() ops. + * + * numa_maps scans all vmas under mmap_sem and checks their mempolicy. + * Each mempolicy object is controlled by reference counting. The problem here + * is how to avoid accessing dead mempolicy object. + * + * Because we're holding mmap_sem while reading seq_file, it's safe to access + * each vma's mempolicy, no vma objects will never drop refs to mempolicy. + * + * A task's mempolicy (task->mempolicy) has different behavior. task->mempolicy + * is set and replaced under mmap_sem but unrefed and cleared under task_lock(). + * So, without task_lock(), we cannot trust get_vma_policy() because we cannot + * gurantee the task never exits under us. But taking task_lock() around + * get_vma_plicy() causes lock order problem. + * + * To access task->mempolicy without lock, we hold a reference count of an + * object pointed by task->mempolicy and remember it. This will guarantee + * that task->mempolicy points to an alive object or NULL in numa_maps accesses. + */ +static void hold_task_mempolicy(struct proc_maps_private *priv) +{ + struct task_struct *task = priv->task; + + task_lock(task); + priv->task_mempolicy = task->mempolicy; + mpol_get(priv->task_mempolicy); + task_unlock(task); +} +static void release_task_mempolicy(struct proc_maps_private *priv) +{ + mpol_put(priv->task_mempolicy); +} +#else +static void hold_task_mempolicy(struct proc_maps_private *priv) +{ +} +static void release_task_mempolicy(struct proc_maps_private *priv) +{ +} +#endif + static void vma_stop(struct proc_maps_private *priv, struct vm_area_struct *vma) { if (vma && vma != priv->tail_vma) { struct mm_struct *mm = vma->vm_mm; + release_task_mempolicy(priv); up_read(&mm->mmap_sem); mmput(mm); } @@ -132,7 +177,7 @@ static void *m_start(struct seq_file *m, loff_t *pos) tail_vma = get_gate_vma(priv->task->mm); priv->tail_vma = tail_vma; - + hold_task_mempolicy(priv); /* Start with last addr hint */ vma = find_vma(mm, last_addr); if (last_addr && vma) { @@ -159,6 +204,7 @@ out: if (vma) return vma; + release_task_mempolicy(priv); /* End of vmas has been reached */ m->version = (tail_vma != NULL)? 0: -1UL; up_read(&mm->mmap_sem); @@ -1178,11 +1224,9 @@ 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); seq_printf(m, "%08lx %s", vma->vm_start, buffer); |