ext4lazyinit is global thread. This thread performs itable initalization under
It basically does followes:
ext4_lazyinit_thread
->mutex_lock(&eli->li_list_mtx);
->ext4_run_li_request(elr)
->ext4_init_inode_table-> Do a lot of IO if list is large
And when new mounts/umount arrives they have to block on ->li_list_mtx
because lazy_thread holds it during full walk procedure.
ext4_fill_super
->ext4_register_li_request
->mutex_lock(&ext4_li_info->li_list_mtx);
->list_add(&elr->lr_request, &ext4_li_info >li_request_list);
In my case mount takes 40minutes on server with 36 * 4Tb HDD.
Convenient user may face this in case of very slow dev ( /dev/mmcblkXXX)
Even more. I one of filesystem was frozen lazyinit_thread will simply blocks
on sb_start_write() so other mount/umounts will suck forever.
This patch changes logic like follows:
- grap ->s_umount read sem before process new li_request after that it is safe
to drop list_mtx because all callers of li_remove_requers are holds ->s_umount
for write.
- li_thread skip frozen SB's
Locking:
Locking order is asserted by umout path like follows: s_umount ->li_list_mtx
so the only way to to grab ->s_mount inside li_thread is via down_read_trylock
xfstests:ext4/022 message-id:1468931005-774-1-git-send-email-dmonakhov@xxxxxxxxxx
#PSBM-49658
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
---
fs/ext4/super.c | 53 ++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 36 insertions(+), 17 deletions(-)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 3822a5a..0ee193f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2635,7 +2635,6 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
sb = elr->lr_super;
ngroups = EXT4_SB(sb)->s_groups_count;
- sb_start_write(sb);
for (group = elr->lr_next_group; group < ngroups; group++) {
gdp = ext4_get_group_desc(sb, group, NULL);
if (!gdp) {
@@ -2662,8 +2661,6 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
elr->lr_next_sched = jiffies + elr->lr_timeout;
elr->lr_next_group = group + 1;
}
- sb_end_write(sb);
-
return ret;
}
@@ -2713,9 +2710,9 @@ static struct task_struct *ext4_lazyinit_task;
static int ext4_lazyinit_thread(void *arg)
{
struct ext4_lazy_init *eli = (struct ext4_lazy_init *)arg;
- struct list_head *pos, *n;
struct ext4_li_request *elr;
unsigned long next_wakeup, cur;
+ LIST_HEAD(request_list);
BUG_ON(NULL == eli);
@@ -2728,21 +2725,43 @@ cont_thread:
mutex_unlock(&eli->li_list_mtx);
goto exit_thread;
}
-
- list_for_each_safe(pos, n, &eli->li_request_list) {
- elr = list_entry(pos, struct ext4_li_request,
- lr_request);
-
- if (time_after_eq(jiffies, elr->lr_next_sched)) {
- if (ext4_run_li_request(elr) != 0) {
- /* error, remove the lazy_init job */
- ext4_remove_li_request(elr);
- continue;
+ list_splice_init(&eli->li_request_list, &request_list);
+ while (!list_empty(&request_list)) {
+ int err = 0;
+ int progress = 0;
+
+ elr = list_entry(request_list.next,
+ struct ext4_li_request, lr_request);
+ list_move(request_list.next, &eli->li_request_list);
+ if (time_before(jiffies, elr->lr_next_sched)) {
+ if (time_before(elr->lr_next_sched, next_wakeup))
+ next_wakeup = elr->lr_next_sched;
+ continue;
+ }
+ if (down_read_trylock(&elr->lr_super->s_umount)) {
+ if (sb_start_write_trylock(elr->lr_super)) {
+ progress = 1;
+ /* We holds sb->s_umount, sb can not
+ * be removed from the list, it is
+ * now safe to drop li_list_mtx
+ */
+ mutex_unlock(&eli->li_list_mtx);
+ err = ext4_run_li_request(elr);
+ sb_end_write(elr->lr_super);
+ mutex_lock(&eli->li_list_mtx);
}
+ up_read((&elr->lr_super->s_umount));
+ }
+ /* error, remove the lazy_init job */
+ if (err) {
+ ext4_remove_li_request(elr);
+ continue;
+ }
+ if (!progress) {
+ elr->lr_next_sched = jiffies +
+ (prandom_u32()
+ % (EXT4_DEF_LI_MAX_START_DELAY * HZ));
}
-
- if (time_before(elr->lr_next_sched, next_wakeup))
- next_wakeup = elr->lr_next_sched;
}
mutex_unlock(&eli->li_list_mtx);
--
1.8.3.1
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