Janak Desai wrote:
- tsk->min_flt = tsk->maj_flt = 0;
- tsk->nvcsw = tsk->nivcsw = 0;
+ /*
+ * If the process memory is being duplicated as part of the
+ * unshare system call, we are working with the current process
+ * and not a newly allocated task strucutre, and should not
+ * zero out fault info, context switch counts, mm and active_mm
+ * fields.
+ */
+ if (copy_share_action == MAY_SHARE) {
+ tsk->min_flt = tsk->maj_flt = 0;
+ tsk->nvcsw = tsk->nivcsw = 0;
Why don't you just do this in copy_process?
- tsk->mm = NULL;
- tsk->active_mm = NULL;
+ tsk->mm = NULL;
+ tsk->active_mm = NULL;
+ }
/*
* Are we cloning a kernel thread?
@@ -1002,7 +1023,7 @@ static task_t *copy_process(unsigned lon
goto bad_fork_cleanup_fs;
if ((retval = copy_signal(clone_flags, p)))
goto bad_fork_cleanup_sighand;
- if ((retval = copy_mm(clone_flags, p)))
+ if ((retval = copy_mm(clone_flags, p, MAY_SHARE)))
goto bad_fork_cleanup_signal;
if ((retval = copy_keys(clone_flags, p)))
goto bad_fork_cleanup_mm;
@@ -1317,3 +1338,172 @@ void __init proc_caches_init(void)
sizeof(struct mm_struct), 0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
}
+
+/*
+ * unshare_mm is called from the unshare system call handler function to
+ * make a private copy of the mm_struct structure. It calls copy_mm with
+ * CLONE_VM flag cleard, to ensure that a private copy of mm_struct is made,
+ * and with mm_copy_share enum set to UNSHARE, to ensure that copy_mm
+ * does not clear fault info, context switch counts, mm and active_mm
+ * fields of the mm_struct.
+ */
+static int unshare_mm(unsigned long unshare_flags, struct task_struct *tsk)
+{
+ int retval = 0;
+ struct mm_struct *mm = tsk->mm;
+
+ /*
+ * If the virtual memory is being shared, make a private
+ * copy and disassociate the process from the shared virtual
+ * memory.
+ */
+ if (atomic_read(&mm->mm_users) > 1) {
+ retval = copy_mm((unshare_flags & ~CLONE_VM), tsk, UNSHARE);
+
+ /*
+ * If copy_mm was successful, decrement the number of users
+ * on the original, shared, mm_struct.
+ */
+ if (!retval)
+ atomic_dec(&mm->mm_users);
+ }
+ return retval;
+}
+
What prevents thread 1 from decrementing mm_users after thread 2 has
found it to be 2?
--
SUSE Labs, Novell Inc.
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