Re: [PATCH 2/2] block: hold queue lock while iterating in diskstats_show

From: Daniel Wagner
Date: Thu Jan 20 2022 - 09:06:34 EST

On Thu, Jan 20, 2022 at 03:01:27PM +0100, Daniel Wagner wrote:
> On Thu, Jan 20, 2022 at 09:51:18PM +0800, Ming Lei wrote:
> > Then Can you figure out where blk_mq_queue_tag_busy_iter+0x1e4 points to
> > in source code? And what is NULL pointer?

Yes %rax is NULL

> Here we go:
>
> /usr/src/debug/kernel-default-5.3.18-59.27.1.x86_64/linux-5.3/linux-obj/../include/linux/sbitmap.h: 249
> 0xffffffffb244a254 <blk_mq_queue_tag_busy_iter+484>: mov (%rax),%rdx
>
> 234static inline void __sbitmap_for_each_set(struct sbitmap *sb,
> 235 unsigned int start,
> 236 sb_for_each_fn fn, void *data)
> 237{
> 238 unsigned int index;
> 239 unsigned int nr;
> 240 unsigned int scanned = 0;
> 241
> 242 if (start >= sb->depth)
> 243 start = 0;
> 244 index = SB_NR_TO_INDEX(sb, start);
> 245 nr = SB_NR_TO_BIT(sb, start);
> 246
> 247 while (scanned < sb->depth) {
> 248 unsigned long word;
> 249 unsigned int depth = min_t(unsigned int,
> 250 sb->map[index].depth - nr,
> 251 sb->depth - scanned);


forgot to add this

crash> bt
PID: 17640 TASK: ffff956f4a468000 CPU: 13 COMMAND: "iostat"
#0 [ffffb701aefb7980] machine_kexec at ffffffffba66fb91
#1 [ffffb701aefb79d8] __crash_kexec at ffffffffba75927d
#2 [ffffb701aefb7aa0] crash_kexec at ffffffffba75a13d
#3 [ffffb701aefb7ab8] oops_end at ffffffffba636cdf
#4 [ffffb701aefb7ad8] no_context at ffffffffba682baf
#5 [ffffb701aefb7b40] do_page_fault at ffffffffba683e30
#6 [ffffb701aefb7b70] page_fault at ffffffffbb0012fe
[exception RIP: blk_mq_queue_tag_busy_iter+484]
RIP: ffffffffbaa4a254 RSP: ffffb701aefb7c20 RFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: ffff954f43c14c00 RSI: ffffffffbaa442c0 RDI: ffff954fb3749010
RBP: 0000000000000000 R8: 0000000800000000 R9: 00000008ffffffff
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff9567b2200000 R14: ffff954798c09bc0 R15: ffff954798c09c20
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#7 [ffffb701aefb7cb0] blk_mq_in_flight at ffffffffbaa461e5
#8 [ffffb701aefb7cd0] diskstats_show at ffffffffbaa4f00d
#9 [ffffb701aefb7e50] seq_read at ffffffffba90df16
#10 [ffffb701aefb7eb0] proc_reg_read at ffffffffba96d789
#11 [ffffb701aefb7ec8] vfs_read at ffffffffba8e4c39
#12 [ffffb701aefb7ef8] ksys_read at ffffffffba8e4fc1
#13 [ffffb701aefb7f38] do_syscall_64 at ffffffffba60538b
#14 [ffffb701aefb7f50] entry_SYSCALL_64_after_hwframe at ffffffffbb00008c
RIP: 00007f6031f4eb5e RSP: 00007ffd187a7e88 RFLAGS: 00000246
RAX: ffffffffffffffda RBX: 00005577a698c2c0 RCX: 00007f6031f4eb5e
RDX: 0000000000000400 RSI: 00005577a698f480 RDI: 0000000000000003
RBP: 00007f603222e300 R8: 0000000000000000 R9: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000a
R13: 0000000000000d68 R14: 00007f603222d700 R15: 0000000000000d68
ORIG_RAX: 0000000000000000 CS: 0033 SS: 002b


I've tried to figure out the request_pointer from the registers and I
think the pointer is still in %rdi

struct request_queue {
last_merge = 0x0,
elevator = 0x0,
stats = 0xffff956f45a9bec0,
rq_qos = 0xffff954f54c57558,
mq_ops = 0xffffffffc0c27140 <nvme_tcp_mq_ops>,
queue_ctx = 0x4151cf2266c0,
queue_depth = 0x0,
queue_hw_ctx = 0xffff954f43c14c00,
nr_hw_queues = 0x50,
backing_dev_info = 0xffff953fae3ae800,
queuedata = 0xffff953622282800,
queue_flags = 0x5041d0,

struct request_queue {
last_merge = 0x0,
elevator = 0x0,
stats = 0xffff956f45a9bec0,
rq_qos = 0xffff954f54c57558,
mq_ops = 0xffffffffc0c27140 <nvme_tcp_mq_ops>,
queue_ctx = 0x4151cf2266c0,
queue_depth = 0x0,
queue_hw_ctx = 0xffff954f43c14c00,
nr_hw_queues = 0x50,
backing_dev_info = 0xffff953fae3ae800,
queuedata = 0xffff953622282800,
queue_flags = 0x5041d0,
pm_only = {
counter = 0x0
},
id = 0x61,
bounce_gfp = 0x0,
queue_lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
kobj = {
name = 0xffffffffbb7846be "queue",
entry = {
next = 0xffff954fb3749088,
prev = 0xffff954fb3749088
},
parent = 0xffff95af629a58a0,
kset = 0x0,
ktype = 0xffffffffbbb56540,
sd = 0xffff956563ecd580,
kref = {
refcount = {
refs = {
counter = 0x2
}
}
},
state_initialized = 0x1,
state_in_sysfs = 0x1,
state_add_uevent_sent = 0x0,
state_remove_uevent_sent = 0x0,
uevent_suppress = 0x0
},
mq_kobj = 0xffff95720ca05660,
integrity = {
profile = 0x0,
flags = 0x0,
tuple_size = 0x0,
interval_exp = 0x0,
tag_size = 0x0
},
dev = 0x0,
rpm_status = RPM_ACTIVE,
nr_pending = 0x0,
nr_requests = 0x80,
dma_pad_mask = 0x0,
dma_alignment = 0x7,
ksm = 0x0,
rq_timeout = 0x1d4c,
poll_nsec = 0xffffffff,
poll_cb = 0xffff953443cafa00,
poll_stat = {{
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}, {
mean = 0x0,
min = 0x0,
max = 0x0,
nr_samples = 0x0,
batch = 0x0
}},
timeout = {
entry = {
next = 0x0,
pprev = 0x0
},
expires = 0x0,
function = 0xffffffffbaa39440,
flags = 0x2c
},
timeout_work = {
data = {
counter = 0xfffffffe0
},
entry = {
next = 0xffff954fb37493c0,
prev = 0xffff954fb37493c0
},
func = 0xffffffffbaa454f0
},
icq_list = {
next = 0xffff954fb37493d8,
prev = 0xffff954fb37493d8
},
blkcg_pols = {0x3},
root_blkg = 0xffff953622281c00,
blkg_list = {
next = 0xffff953622281c08,
prev = 0xffff953622281c08
},
limits = {
bounce_pfn = 0xfffffffffffff,
seg_boundary_mask = 0xffffffff,
virt_boundary_mask = 0xfff,
max_hw_sectors = 0x800,
max_dev_sectors = 0x0,
chunk_sectors = 0x0,
max_sectors = 0x800,
max_segment_size = 0xffffffff,
physical_block_size = 0x200,
logical_block_size = 0x200,
alignment_offset = 0x0,
io_min = 0x200,
io_opt = 0x0,
max_discard_sectors = 0xffffffff,
max_hw_discard_sectors = 0xffffffff,
max_write_same_sectors = 0x0,
max_write_zeroes_sectors = 0x801,
max_zone_append_sectors = 0x0,
discard_granularity = 0x200,
discard_alignment = 0x0,
max_segments = 0x101,
max_integrity_segments = 0x0,
max_discard_segments = 0x100,
misaligned = 0x0,
discard_misaligned = 0x0,
raid_partial_stripes_expensive = 0x0,
zoned = BLK_ZONED_NONE
},
required_elevator_features = 0x0,
nr_zones = 0x0,
conv_zones_bitmap = 0x0,
seq_zones_wlock = 0x0,
sg_timeout = 0x0,
sg_reserved_size = 0x7fffffff,
node = 0xffffffff,
blk_trace = 0x0,
blk_trace_mutex = {
owner = {
counter = 0x0
},
wait_lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
osq = {
tail = {
counter = 0x0
}
},
wait_list = {
next = 0xffff954fb37494b8,
prev = 0xffff954fb37494b8
}
},
fq = 0x0,
requeue_list = {
next = 0xffff954fb37494d0,
prev = 0xffff954fb37494d0
},
requeue_lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
requeue_work = {
work = {
data = {
counter = 0xfffffffe0
},
entry = {
next = 0xffff954fb37494f0,
prev = 0xffff954fb37494f0
},
func = 0xffffffffbaa474d0
},
timer = {
entry = {
next = 0x0,
pprev = 0x0
},
expires = 0x0,
function = 0xffffffffba6bb050,
flags = 0x200040
},
wq = 0x0,
cpu = 0x0
},
sysfs_lock = {
owner = {
counter = 0x0
},
wait_lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
osq = {
tail = {
counter = 0x0
}
},
wait_list = {
next = 0xffff954fb3749550,
prev = 0xffff954fb3749550
}
},
sysfs_dir_lock = {
owner = {
counter = 0x0
},
wait_lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
osq = {
tail = {
counter = 0x0
}
},
wait_list = {
next = 0xffff954fb3749570,
prev = 0xffff954fb3749570
}
},
unused_hctx_list = {
next = 0xffff954fb3749580,
prev = 0xffff954fb3749580
},
unused_hctx_lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
mq_freeze_depth = 0x0,
bsg_dev = {
class_dev = 0x0,
minor = 0x0,
queue = 0x0,
ops = 0x0
},
td = 0xffff954f43c12800,
callback_head = {
next = 0x0,
func = 0x0
},
mq_freeze_wq = {
lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
head = {
next = 0xffff954fb37495d8,
prev = 0xffff954fb37495d8
}
},
mq_freeze_lock = {
owner = {
counter = 0x0
},
wait_lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
osq = {
tail = {
counter = 0x0
}
},
wait_list = {
next = 0xffff954fb37495f8,
prev = 0xffff954fb37495f8
}
},
q_usage_counter = {
count = {
counter = 0x8000000000000001
},
percpu_count_ptr = 0x4151cda18fe8,
release = 0xffffffffbaa38da0,
confirm_switch = 0x0,
force_atomic = 0x0,
allow_reinit = 0x1,
rcu = {
next = 0x0,
func = 0x0
}
},
tag_set = 0xffff958f7fe56008,
tag_set_list = {
next = 0xffff958f7fe56118,
prev = 0xffff956f479e6ea0
},
bio_split = {
bio_slab = 0xffff9530c7c20e00,
front_pad = 0x0,
bio_pool = {
lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
min_nr = 0x2,
curr_nr = 0x2,
elements = 0xffff954fbdb45180,
pool_data = 0xffff9530c7c20e00,
alloc = 0xffffffffba832460,
free = 0xffffffffba832480,
wait = {
lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
head = {
next = 0xffff954fb37496a0,
prev = 0xffff954fb37496a0
}
}
},
bvec_pool = {
lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
min_nr = 0x2,
curr_nr = 0x2,
elements = 0xffff954fbdb453f0,
pool_data = 0xffff956fbe9a9180,
alloc = 0xffffffffba832460,
free = 0xffffffffba832480,
wait = {
lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
head = {
next = 0xffff954fb37496e8,
prev = 0xffff954fb37496e8
}
}
},
bio_integrity_pool = {
lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
min_nr = 0x0,
curr_nr = 0x0,
elements = 0x0,
pool_data = 0x0,
alloc = 0x0,
free = 0x0,
wait = {
lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
head = {
next = 0x0,
prev = 0x0
}
}
},
bvec_integrity_pool = {
lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
min_nr = 0x0,
curr_nr = 0x0,
elements = 0x0,
pool_data = 0x0,
alloc = 0x0,
free = 0x0,
wait = {
lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
head = {
next = 0x0,
prev = 0x0
}
}
},
rescue_lock = {
{
rlock = {
raw_lock = {
{
val = {
counter = 0x0
},
{
locked = 0x0,
pending = 0x0
},
{
locked_pending = 0x0,
tail = 0x0
}
}
}
}
}
},
rescue_list = {
head = 0x0,
tail = 0x0
},
rescue_work = {
data = {
counter = 0xfffffffe0
},
entry = {
next = 0xffff954fb37497a8,
prev = 0xffff954fb37497a8
},
func = 0xffffffffbaa33ec0
},
rescue_workqueue = 0x0
},
debugfs_dir = 0xffff956f64d2efc0,
sched_debugfs_dir = 0x0,
rqos_debugfs_dir = 0xffff953fae3a6d80,
mq_sysfs_init_done = 0x1,
cmd_size = 0x0,
write_hints = {0x0, 0x0, 0x0, 0x0, 0x0}
}