Messages in this thread Patch in this message | | | Date | Fri, 10 Jul 2009 03:27:38 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 1/2] mm_for_maps: shift down_read(mmap_sem) to the caller |
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mm_for_maps() takes ->mmap_sem after security checks, this looks strange and obfuscates the locking rules. Move this lock to its single caller, m_start().
Signed-off-by: Oleg Nesterov <oleg@redhat.com> ---
fs/proc/task_mmu.c | 1 + fs/proc/task_nommu.c | 1 + fs/proc/base.c | 8 +++----- 3 files changed, 5 insertions(+), 5 deletions(-)
--- WAIT/fs/proc/task_mmu.c~1_MOVE_MMAP_SEM 2009-05-03 17:15:27.000000000 +0200 +++ WAIT/fs/proc/task_mmu.c 2009-07-10 02:00:56.000000000 +0200 @@ -119,6 +119,7 @@ static void *m_start(struct seq_file *m, mm = mm_for_maps(priv->task); if (!mm) return NULL; + down_read(&mm->mmap_sem); tail_vma = get_gate_vma(priv->task); priv->tail_vma = tail_vma; --- WAIT/fs/proc/task_nommu.c~1_MOVE_MMAP_SEM 2009-04-09 00:39:09.000000000 +0200 +++ WAIT/fs/proc/task_nommu.c 2009-07-10 02:01:25.000000000 +0200 @@ -189,6 +189,7 @@ static void *m_start(struct seq_file *m, priv->task = NULL; return NULL; } + down_read(&mm->mmap_sem); /* start from the Nth VMA */ for (p = rb_first(&mm->mm_rb); p; p = rb_next(p)) --- WAIT/fs/proc/base.c~1_MOVE_MMAP_SEM 2009-07-09 17:56:27.000000000 +0200 +++ WAIT/fs/proc/base.c 2009-07-10 02:05:14.000000000 +0200 @@ -235,9 +235,8 @@ static int check_mem_permission(struct t struct mm_struct *mm_for_maps(struct task_struct *task) { struct mm_struct *mm = get_task_mm(task); - if (!mm) - return NULL; - if (mm != current->mm) { + + if (mm && mm != current->mm) { /* * task->mm can be changed before security check, * in that case we must notice the change after. @@ -245,10 +244,9 @@ struct mm_struct *mm_for_maps(struct tas if (!ptrace_may_access(task, PTRACE_MODE_READ) || mm != task->mm) { mmput(mm); - return NULL; + mm = NULL; } } - down_read(&mm->mmap_sem); return mm; }
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