Re: [RFC 05/18] limits: track and present RLIMIT_NOFILE actual max

[Andy Lutomirski]

On 06/13/2016 12:44 PM, Topi Miettinen wrote:
Track maximum number of files for the process, present current maximum
in /proc/self/limits.

The core part should be its own patch.

Also, you have this weirdly named (and racy!) function bump_rlimit. 
Wouldn't this be nicer if you taught the rlimit code to track the 
*current* usage generically and to derive the max usage from that?

diff --git a/fs/proc/base.c b/fs/proc/base.c
index a11eb71..227997b 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -630,8 +630,8 @@ static int proc_pid_limits(struct seq_file *m, struct 
pid_namespace *ns,
        /*
         * print the file header
         */
-       seq_printf(m, "%-25s %-20s %-20s %-10s\n",
-                 "Limit", "Soft Limit", "Hard Limit", "Units");
+       seq_printf(m, "%-25s %-20s %-20s %-10s %-20s\n",
+                  "Limit", "Soft Limit", "Hard Limit", "Units", "Max");

What existing programs, if any, does this break?


        for (i = 0; i < RLIM_NLIMITS; i++) {
                if (rlim[i].rlim_cur == RLIM_INFINITY)
@@ -647,9 +647,11 @@ static int proc_pid_limits(struct seq_file *m, struct 
pid_namespace *ns,
                        seq_printf(m, "%-20lu ", rlim[i].rlim_max);

                if (lnames[i].unit)
-                       seq_printf(m, "%-10s\n", lnames[i].unit);
+                       seq_printf(m, "%-10s", lnames[i].unit);
                else
-                       seq_putc(m, '\n');
+                       seq_printf(m, "%-10s", "");
+               seq_printf(m, "%-20lu\n",
+                          task->signal->rlim_curmax[i]);
        }

        return 0;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9c48a08..0150380 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -782,6 +782,7 @@ struct signal_struct {
         * have no need to disable irqs.
         */
        struct rlimit rlim[RLIM_NLIMITS];
+       unsigned long rlim_curmax[RLIM_NLIMITS];

 #ifdef CONFIG_BSD_PROCESS_ACCT
        struct pacct_struct pacct;      /* per-process accounting information */
@@ -3376,6 +3377,12 @@ static inline unsigned long rlimit_max(unsigned int 
limit)
        return task_rlimit_max(current, limit);
 }

+static inline void bump_rlimit(unsigned int limit, unsigned long r)
+{
+       if (READ_ONCE(current->signal->rlim_curmax[limit]) < r)
+               current->signal->rlim_curmax[limit] = r;
+}
+
 #ifdef CONFIG_CPU_FREQ
 struct update_util_data {
        void (*func)(struct update_util_data *data,