On 12/11/18 6:05 PM, Jens Axboe wrote:
> On 12/11/18 5:38 PM, Ming Lei wrote:
>> On Wed, Dec 12, 2018 at 8:28 AM Mike Snitzer <[email protected]> wrote:
>>>
>>> On Tue, Dec 11 2018 at 7:19pm -0500,
>>> Ming Lei <[email protected]> wrote:
>>>
>>>> On Wed, Dec 12, 2018 at 8:04 AM Jens Axboe <[email protected]> wrote:
>>>>>
>>>>> On 12/11/18 3:58 PM, Bart Van Assche wrote:
>>>>>> Hi Jens,
>>>>>>
>>>>>> If I run the following subset of blktests:
>>>>>>
>>>>>> while :; do ./check -q srp && ./check -q nvmeof-mp; done
>>>>>>
>>>>>> against today's for-next branch (commit dd2bf2df85a7) then after some
>>>>>> time the following hang is reported:
>>>>>>
>>>>>> INFO: task fio:14869 blocked for more than 120 seconds.
>>>>>> Not tainted 4.20.0-rc6-dbg+ #1
>>>>>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>>>>> fio D25272 14869 14195 0x00000000
>>>>>> Call Trace:
>>>>>> __schedule+0x401/0xe50
>>>>>> schedule+0x4e/0xd0
>>>>>> io_schedule+0x21/0x50
>>>>>> blk_mq_get_tag+0x46d/0x640
>>>>>> blk_mq_get_request+0x7c0/0xa00
>>>>>> blk_mq_make_request+0x241/0xa70
>>>>>> generic_make_request+0x411/0x950
>>>>>> submit_bio+0x9b/0x250
>>>>>> blkdev_direct_IO+0x7fb/0x870
>>>>>> generic_file_direct_write+0x119/0x210
>>>>>> __generic_file_write_iter+0x11c/0x280
>>>>>> blkdev_write_iter+0x13c/0x220
>>>>>> aio_write+0x204/0x310
>>>>>> io_submit_one+0x9c6/0xe70
>>>>>> __x64_sys_io_submit+0x115/0x340
>>>>>> do_syscall_64+0x71/0x210
>>>>>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>>>>
>>>>>> When that hang occurs my list-pending-block-requests script does not show
>>>>>> any pending requests:
>>>>>>
>>>>>> # list-pending-block-requests
>>>>>> dm-0
>>>>>> loop0
>>>>>> loop1
>>>>>> loop2
>>>>>> loop3
>>>>>> loop4
>>>>>> loop5
>>>>>> loop6
>>>>>> loop7
>>>>>> nullb0
>>>>>> nullb1
>>>>>> sda
>>>>>> sdb
>>>>>> sdc
>>>>>> sdd
>>>>>> vda
>>>>>> vdb
>>>>>>
>>>>>> Enabling fail_if_no_path mode did not resolve the hang so I don't think
>>>>>> that the root cause is in any of the dm drivers used in this test:
>>>>>>
>>>>>> # dmsetup ls | while read dm rest; do dmsetup message $dm 0
>>>>>> fail_if_no_path; done; dmsetup remove_all; dmsetup table
>>>>>> 360014056e756c6c62300000000000000: 0 65536 multipath 0 1 alua 1 1
>>>>>> service-time 0 1 2 8:16 1 1
>>>>>>
>>>>>> The same test passes against kernel v4.20-rc6.
>>>>>
>>>>> What device is this being run on?
>>>>
>>>> I saw this issue on usb storage too.
>>>>
>>>> Seems it is introduced by commit ea86ea2cdced ("sbitmap: ammortize cost of
>>>> clearing bits"). When the IO hang happens, .cleared is 2, and .busy is 0 on
>>>> the sched_tag's sbitmap queue.
>>>
>>> You saw this running the same tests as Bart?
>>
>> Not the srp test as done by Bart, I just run 'parted' test on usb storage
>> disk,
>> see the attached test script.
>>
>> Mostly it can be triggered in one run, sometimes it needs more.
>
> I'll take a look. The ->cleared doesn't make sense for QD=1, or on
> one word in general. But I'd like to try and understand why it hangs.
>
> Are you using a scheduler?
OK, I think I see what it is, the shallow is missing the deferred clear.
On top of this, probably worth to check at what depths deferred starts
to make sense. For QD == 1, definitely not. But that should be on top of
the fix.
Can you try this one?
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 2261136ae067..d98ba7af6bce 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -20,6 +20,47 @@
#include <linux/sbitmap.h>
#include <linux/seq_file.h>
+/*
+ * See if we have deferred clears that we can batch move
+ */
+static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
+{
+ unsigned long mask, val;
+ unsigned long __maybe_unused flags;
+ bool ret = false;
+
+ /* Silence bogus lockdep warning */
+#if defined(CONFIG_LOCKDEP)
+ local_irq_save(flags);
+#endif
+ spin_lock(&sb->map[index].swap_lock);
+
+ if (!sb->map[index].cleared)
+ goto out_unlock;
+
+ /*
+ * First get a stable cleared mask, setting the old mask to 0.
+ */
+ do {
+ mask = sb->map[index].cleared;
+ } while (cmpxchg(&sb->map[index].cleared, mask, 0) != mask);
+
+ /*
+ * Now clear the masked bits in our free word
+ */
+ do {
+ val = sb->map[index].word;
+ } while (cmpxchg(&sb->map[index].word, val, val & ~mask) != val);
+
+ ret = true;
+out_unlock:
+ spin_unlock(&sb->map[index].swap_lock);
+#if defined(CONFIG_LOCKDEP)
+ local_irq_restore(flags);
+#endif
+ return ret;
+}
+
int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
gfp_t flags, int node)
{
@@ -70,6 +111,9 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
unsigned int bits_per_word = 1U << sb->shift;
unsigned int i;
+ for (i = 0; i < sb->map_nr; i++)
+ sbitmap_deferred_clear(sb, i);
+
sb->depth = depth;
sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
@@ -112,47 +156,6 @@ static int __sbitmap_get_word(unsigned long *word,
unsigned long depth,
return nr;
}
-/*
- * See if we have deferred clears that we can batch move
- */
-static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
-{
- unsigned long mask, val;
- unsigned long __maybe_unused flags;
- bool ret = false;
-
- /* Silence bogus lockdep warning */
-#if defined(CONFIG_LOCKDEP)
- local_irq_save(flags);
-#endif
- spin_lock(&sb->map[index].swap_lock);
-
- if (!sb->map[index].cleared)
- goto out_unlock;
-
- /*
- * First get a stable cleared mask, setting the old mask to 0.
- */
- do {
- mask = sb->map[index].cleared;
- } while (cmpxchg(&sb->map[index].cleared, mask, 0) != mask);
-
- /*
- * Now clear the masked bits in our free word
- */
- do {
- val = sb->map[index].word;
- } while (cmpxchg(&sb->map[index].word, val, val & ~mask) != val);
-
- ret = true;
-out_unlock:
- spin_unlock(&sb->map[index].swap_lock);
-#if defined(CONFIG_LOCKDEP)
- local_irq_restore(flags);
-#endif
- return ret;
-}
-
static int sbitmap_find_bit_in_index(struct sbitmap *sb, int index,
unsigned int alloc_hint, bool round_robin)
{
@@ -215,6 +218,7 @@ int sbitmap_get_shallow(struct sbitmap *sb, unsigned int
alloc_hint,
index = SB_NR_TO_INDEX(sb, alloc_hint);
for (i = 0; i < sb->map_nr; i++) {
+again:
nr = __sbitmap_get_word(&sb->map[index].word,
min(sb->map[index].depth,
shallow_depth),
SB_NR_TO_BIT(sb, alloc_hint), true);
@@ -223,6 +227,9 @@ int sbitmap_get_shallow(struct sbitmap *sb, unsigned int
alloc_hint,
break;
}
+ if (sbitmap_deferred_clear(sb, index))
+ goto again;
+
/* Jump to next index. */
index++;
alloc_hint = index << sb->shift;
--
Jens Axboe
