task IO accounting: correctly account threads IO statistics

Oleg Nesterov points out that we should check that the task is still alive
before we iterate over the threads.  This patch includes a fixup for this.

Also simplify do_io_accounting() implementation.

Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 81bce6791bfc3cccd000309c53cd328b6cfc7425..d744aa3c9f746ac527b4c1d6e46f8d625bc69f78 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2406,35 +2406,18 @@ static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
        u64 rchar, wchar, syscr, syscw;
        struct task_io_accounting ioac;
 
-       if (!whole) {
-               rchar = task->rchar;
-               wchar = task->wchar;
-               syscr = task->syscr;
-               syscw = task->syscw;
-               memcpy(&ioac, &task->ioac, sizeof(ioac));
-       } else {
-               unsigned long flags;
-               struct task_struct *t = task;
-               rchar = wchar = syscr = syscw = 0;
-               memset(&ioac, 0, sizeof(ioac));
+       rchar = task->rchar;
+       wchar = task->wchar;
+       syscr = task->syscr;
+       syscw = task->syscw;
+       memcpy(&ioac, &task->ioac, sizeof(ioac));
 
-               rcu_read_lock();
-               do {
-                       rchar += t->rchar;
-                       wchar += t->wchar;
-                       syscr += t->syscr;
-                       syscw += t->syscw;
-
-                       ioac.read_bytes += t->ioac.read_bytes;
-                       ioac.write_bytes += t->ioac.write_bytes;
-                       ioac.cancelled_write_bytes +=
-                                       t->ioac.cancelled_write_bytes;
-                       t = next_thread(t);
-               } while (t != task);
-               rcu_read_unlock();
+       if (whole) {
+               unsigned long flags;
 
                if (lock_task_sighand(task, &flags)) {
                        struct signal_struct *sig = task->signal;
+                       struct task_struct *t = task;
 
                        rchar += sig->rchar;
                        wchar += sig->wchar;
@@ -2445,11 +2428,20 @@ static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
                        ioac.write_bytes += sig->ioac.write_bytes;
                        ioac.cancelled_write_bytes +=
                                        sig->ioac.cancelled_write_bytes;
-
+                       while_each_thread(task, t) {
+                               rchar += t->rchar;
+                               wchar += t->wchar;
+                               syscr += t->syscr;
+                               syscw += t->syscw;
+
+                               ioac.read_bytes += t->ioac.read_bytes;
+                               ioac.write_bytes += t->ioac.write_bytes;
+                               ioac.cancelled_write_bytes +=
+                                       t->ioac.cancelled_write_bytes;
+                       }
                        unlock_task_sighand(task, &flags);
                }
        }
-
        return sprintf(buffer,
                        "rchar: %llu\n"
                        "wchar: %llu\n"
@@ -2458,13 +2450,9 @@ static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
                        "read_bytes: %llu\n"
                        "write_bytes: %llu\n"
                        "cancelled_write_bytes: %llu\n",
-                       (unsigned long long)rchar,
-                       (unsigned long long)wchar,
-                       (unsigned long long)syscr,
-                       (unsigned long long)syscw,
-                       (unsigned long long)ioac.read_bytes,
-                       (unsigned long long)ioac.write_bytes,
-                       (unsigned long long)ioac.cancelled_write_bytes);
+                       rchar, wchar, syscr, syscw,
+                       ioac.read_bytes, ioac.write_bytes,
+                       ioac.cancelled_write_bytes);
 }
 
 static int proc_tid_io_accounting(struct task_struct *task, char *buffer)