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authorOleg Nesterov <oleg@redhat.com>2024-01-23 16:33:57 +0100
committerAndrew Morton <akpm@linux-foundation.org>2024-02-07 21:20:33 -0800
commit7601df8031fd67310af891897ef6cc0df4209305 (patch)
treeede6b84c438d11b00d632086a15ca3900c98671e /fs
parent60f92acb60a989b14e4b744501a0df0f82ef30a3 (diff)
fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats
lock_task_sighand() can trigger a hard lockup. If NR_CPUS threads call do_task_stat() at the same time and the process has NR_THREADS, it will spin with irqs disabled O(NR_CPUS * NR_THREADS) time. Change do_task_stat() to use sig->stats_lock to gather the statistics outside of ->siglock protected section, in the likely case this code will run lockless. Link: https://lkml.kernel.org/r/20240123153357.GA21857@redhat.com Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Dylan Hatch <dylanbhatch@google.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/proc/array.c58
1 files changed, 32 insertions, 26 deletions
diff --git a/fs/proc/array.c b/fs/proc/array.c
index 45ba91863808..34a47fb0c57f 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -477,13 +477,13 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
int permitted;
struct mm_struct *mm;
unsigned long long start_time;
- unsigned long cmin_flt = 0, cmaj_flt = 0;
- unsigned long min_flt = 0, maj_flt = 0;
- u64 cutime, cstime, utime, stime;
- u64 cgtime, gtime;
+ unsigned long cmin_flt, cmaj_flt, min_flt, maj_flt;
+ u64 cutime, cstime, cgtime, utime, stime, gtime;
unsigned long rsslim = 0;
unsigned long flags;
int exit_code = task->exit_code;
+ struct signal_struct *sig = task->signal;
+ unsigned int seq = 1;
state = *get_task_state(task);
vsize = eip = esp = 0;
@@ -511,12 +511,8 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
sigemptyset(&sigign);
sigemptyset(&sigcatch);
- cutime = cstime = 0;
- cgtime = gtime = 0;
if (lock_task_sighand(task, &flags)) {
- struct signal_struct *sig = task->signal;
-
if (sig->tty) {
struct pid *pgrp = tty_get_pgrp(sig->tty);
tty_pgrp = pid_nr_ns(pgrp, ns);
@@ -527,27 +523,9 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
num_threads = get_nr_threads(task);
collect_sigign_sigcatch(task, &sigign, &sigcatch);
- cmin_flt = sig->cmin_flt;
- cmaj_flt = sig->cmaj_flt;
- cutime = sig->cutime;
- cstime = sig->cstime;
- cgtime = sig->cgtime;
rsslim = READ_ONCE(sig->rlim[RLIMIT_RSS].rlim_cur);
- /* add up live thread stats at the group level */
if (whole) {
- struct task_struct *t;
-
- __for_each_thread(sig, t) {
- min_flt += t->min_flt;
- maj_flt += t->maj_flt;
- gtime += task_gtime(t);
- }
-
- min_flt += sig->min_flt;
- maj_flt += sig->maj_flt;
- gtime += sig->gtime;
-
if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED))
exit_code = sig->group_exit_code;
}
@@ -562,6 +540,34 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
if (permitted && (!whole || num_threads < 2))
wchan = !task_is_running(task);
+ do {
+ seq++; /* 2 on the 1st/lockless path, otherwise odd */
+ flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq);
+
+ cmin_flt = sig->cmin_flt;
+ cmaj_flt = sig->cmaj_flt;
+ cutime = sig->cutime;
+ cstime = sig->cstime;
+ cgtime = sig->cgtime;
+
+ if (whole) {
+ struct task_struct *t;
+
+ min_flt = sig->min_flt;
+ maj_flt = sig->maj_flt;
+ gtime = sig->gtime;
+
+ rcu_read_lock();
+ __for_each_thread(sig, t) {
+ min_flt += t->min_flt;
+ maj_flt += t->maj_flt;
+ gtime += task_gtime(t);
+ }
+ rcu_read_unlock();
+ }
+ } while (need_seqretry(&sig->stats_lock, seq));
+ done_seqretry_irqrestore(&sig->stats_lock, seq, flags);
+
if (whole) {
thread_group_cputime_adjusted(task, &utime, &stime);
} else {