ext4: prevent an infinite loop in the lazyinit thread

Use ktime_get_ns instead of ktime_get_real_ns when computing the lr_timeout
not to be affected by system time jumps.

Use a boolean instead of the MAX_JIFFY_OFFSET value to determine whether
the next_wakeup value has been set. Comparing elr->lr_next_sched to
MAX_JIFFY_OFFSET can cause the lazyinit thread to loop indefinitely.

Co-developed-by: Lukas Skupinski <lukas.skupinski@landisgyr.com>
Signed-off-by: Lukas Skupinski <lukas.skupinski@landisgyr.com>
Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20241106134741.26948-2-othacehe@gnu.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 33a81ef3c08a17f93dabca7aeb573cd054033c4a..a09f4621b10df8b043afed66dc91ab969e85ba28 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3719,12 +3719,12 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
                ret = 1;
 
        if (!ret) {
-               start_time = ktime_get_real_ns();
+               start_time = ktime_get_ns();
                ret = ext4_init_inode_table(sb, group,
                                            elr->lr_timeout ? 0 : 1);
                trace_ext4_lazy_itable_init(sb, group);
                if (elr->lr_timeout == 0) {
-                       elr->lr_timeout = nsecs_to_jiffies((ktime_get_real_ns() - start_time) *
+                       elr->lr_timeout = nsecs_to_jiffies((ktime_get_ns() - start_time) *
                                EXT4_SB(elr->lr_super)->s_li_wait_mult);
                }
                elr->lr_next_sched = jiffies + elr->lr_timeout;
@@ -3784,8 +3784,9 @@ static int ext4_lazyinit_thread(void *arg)
 
 cont_thread:
        while (true) {
-               next_wakeup = MAX_JIFFY_OFFSET;
+               bool next_wakeup_initialized = false;
 
+               next_wakeup = 0;
                mutex_lock(&eli->li_list_mtx);
                if (list_empty(&eli->li_request_list)) {
                        mutex_unlock(&eli->li_list_mtx);
@@ -3798,8 +3799,11 @@ cont_thread:
                                         lr_request);
 
                        if (time_before(jiffies, elr->lr_next_sched)) {
-                               if (time_before(elr->lr_next_sched, next_wakeup))
+                               if (!next_wakeup_initialized ||
+                                   time_before(elr->lr_next_sched, next_wakeup)) {
                                        next_wakeup = elr->lr_next_sched;
+                                       next_wakeup_initialized = true;
+                               }
                                continue;
                        }
                        if (down_read_trylock(&elr->lr_super->s_umount)) {
@@ -3827,16 +3831,18 @@ cont_thread:
                                elr->lr_next_sched = jiffies +
                                        get_random_u32_below(EXT4_DEF_LI_MAX_START_DELAY * HZ);
                        }
-                       if (time_before(elr->lr_next_sched, next_wakeup))
+                       if (!next_wakeup_initialized ||
+                           time_before(elr->lr_next_sched, next_wakeup)) {
                                next_wakeup = elr->lr_next_sched;
+                               next_wakeup_initialized = true;
+                       }
                }
                mutex_unlock(&eli->li_list_mtx);
 
                try_to_freeze();
 
                cur = jiffies;
-               if ((time_after_eq(cur, next_wakeup)) ||
-                   (MAX_JIFFY_OFFSET == next_wakeup)) {
+               if (!next_wakeup_initialized || time_after_eq(cur, next_wakeup)) {
                        cond_resched();
                        continue;
                }