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>

1 files changed, 22 insertions, 34 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 81bce6791bfc..d744aa3c9f74 100644
--- 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)