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mm: rcu-protected get_mm_exe_file()

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This patch removes mm->mmap_sem from mm->exe_file read side.
Also it kills dup_mm_exe_file() and moves exe_file duplication into
dup_mmap() where both mmap_sems are locked.

[akpm@linux-foundation.org: fix comment typo]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Konstantin Khlebnikov
2015-04-16 12:47:56 -07:00
committed by Linus Torvalds
parent 0ec62afeb1
commit 90f31d0ea8
4 changed files with 40 additions and 22 deletions
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56
kernel/fork.c
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@@ -403,6 +403,9 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
*/
down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
/* No ordering required: file already has been exposed. */
RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
mm->total_vm = oldmm->total_vm;
mm->shared_vm = oldmm->shared_vm;
mm->exec_vm = oldmm->exec_vm;
@@ -528,7 +531,13 @@ static inline void mm_free_pgd(struct mm_struct *mm)
pgd_free(mm, mm->pgd);
}
#else
#define dup_mmap(mm, oldmm) (0)
static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
{
down_write(&oldmm->mmap_sem);
RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
up_write(&oldmm->mmap_sem);
return 0;
}
#define mm_alloc_pgd(mm) (0)
#define mm_free_pgd(mm)
#endif /* CONFIG_MMU */
@@ -697,35 +706,46 @@ void mmput(struct mm_struct *mm)
}
EXPORT_SYMBOL_GPL(mmput);
/**
* set_mm_exe_file - change a reference to the mm's executable file
*
* This changes mm's executable file (shown as symlink /proc/[pid]/exe).
*
* Main users are mmput(), sys_execve() and sys_prctl(PR_SET_MM_MAP/EXE_FILE).
* Callers prevent concurrent invocations: in mmput() nobody alive left,
* in execve task is single-threaded, prctl holds mmap_sem exclusively.
*/
void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
{
struct file *old_exe_file = rcu_dereference_protected(mm->exe_file,
!atomic_read(&mm->mm_users) || current->in_execve ||
lockdep_is_held(&mm->mmap_sem));
if (new_exe_file)
get_file(new_exe_file);
if (mm->exe_file)
fput(mm->exe_file);
mm->exe_file = new_exe_file;
rcu_assign_pointer(mm->exe_file, new_exe_file);
if (old_exe_file)
fput(old_exe_file);
}
/**
* get_mm_exe_file - acquire a reference to the mm's executable file
*
* Returns %NULL if mm has no associated executable file.
* User must release file via fput().
*/
struct file *get_mm_exe_file(struct mm_struct *mm)
{
struct file *exe_file;
/* We need mmap_sem to protect against races with removal of exe_file */
down_read(&mm->mmap_sem);
exe_file = mm->exe_file;
if (exe_file)
get_file(exe_file);
up_read(&mm->mmap_sem);
rcu_read_lock();
exe_file = rcu_dereference(mm->exe_file);
if (exe_file && !get_file_rcu(exe_file))
exe_file = NULL;
rcu_read_unlock();
return exe_file;
}
static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
{
/* It's safe to write the exe_file pointer without exe_file_lock because
* this is called during fork when the task is not yet in /proc */
newmm->exe_file = get_mm_exe_file(oldmm);
}
/**
* get_task_mm - acquire a reference to the task's mm
*
@@ -887,8 +907,6 @@ static struct mm_struct *dup_mm(struct task_struct *tsk)
if (!mm_init(mm, tsk))
goto fail_nomem;
dup_mm_exe_file(oldmm, mm);
err = dup_mmap(mm, oldmm);
if (err)
goto free_pt;