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  1. 29 Aug, 2019 27 commits
  3. 27 Aug, 2019 13 commits
    • Jens Axboe's avatar
      Merge branch 'md-next' of git://git.kernel.org/pub/scm/linux/kernel/git/song/md into for-5.4/block · da8c8281
      Jens Axboe authored 
      Pull MD fixes from Song.

* 'md-next' of git://git.kernel.org/pub/scm/linux/kernel/git/song/md:
  raid5 improve too many read errors msg by adding limits
  md: don't report active array_state until after revalidate_disk() completes.
  md: only call set_in_sync() when it is expected to succeed.
      da8c8281
    • Nigel Croxon's avatar
      raid5 improve too many read errors msg by adding limits · 0009fad0
      Nigel Croxon authored 
      Often limits can be changed by admin. When discussing such things
it helps if you can provide "self-sustained" facts. Also
sometimes the admin thinks he changed a limit, but it did not
take effect for some reason or he changed the wrong thing.

V3: Only pr_warn when Faulty is 0.
V2: Add read_errors value to pr_warn.
Signed-off-by: default avatarNigel Croxon <ncroxon@redhat.com>
Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
      0009fad0
    • NeilBrown's avatar
      md: don't report active array_state until after revalidate_disk() completes. · 9d4b45d6
      NeilBrown authored 
      Until revalidate_disk() has completed, the size of a new md array will
appear to be zero.
So we shouldn't report, through array_state, that the array is active
until that time.
udev rules check array_state to see if the array is ready.  As soon as
it appear to be zero, fsck can be run.  If it find the size to be
zero, it will fail.

So add a new flag to provide an interlock between do_md_run() and
array_state_show().  This flag is set while do_md_run() is active and
it prevents array_state_show() from reporting that the array is
active.

Before do_md_run() is called, ->pers will be NULL so array is
definitely not active.
After do_md_run() is called, revalidate_disk() will have run and the
array will be completely ready.

We also move various sysfs_notify*() calls out of md_run() into
do_md_run() after MD_NOT_READY is cleared.  This ensure the
information is ready before the notification is sent.

Prior to v4.12, array_state_show() was called with the
mddev->reconfig_mutex held, which provided exclusion with do_md_run().

Note that MD_NOT_READY cleared twice.  This is deliberate to cover
both success and error paths with minimal noise.

Fixes: b7b17c9b ("md: remove mddev_lock() from md_attr_show()")
Cc: stable@vger.kernel.org (v4.12++)
Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
      9d4b45d6
    • NeilBrown's avatar
      md: only call set_in_sync() when it is expected to succeed. · 480523fe
      NeilBrown authored 
      Since commit 4ad23a97 ("MD: use per-cpu counter for
writes_pending"), set_in_sync() is substantially more expensive: it
can wait for a full RCU grace period which can be 10s of milliseconds.

So we should only call it when the cost is justified.

md_check_recovery() currently calls set_in_sync() every time it finds
anything to do (on non-external active arrays).  For an array
performing resync or recovery, this will be quite often.
Each call will introduce a delay to the md thread, which can noticeable
affect IO submission latency.

In md_check_recovery() we only need to call set_in_sync() if
'safemode' was non-zero at entry, meaning that there has been not
recent IO.  So we save this "safemode was nonzero" state, and only
call set_in_sync() if it was non-zero.

This measurably reduces mean and maximum IO submission latency during
resync/recovery.
Reported-and-tested-by: default avatarJack Wang <jinpu.wang@cloud.ionos.com>
Fixes: 4ad23a97 ("MD: use per-cpu counter for writes_pending")
Cc: stable@vger.kernel.org (v4.12+)
Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
      480523fe
    • Ming Lei's avatar
      block: split .sysfs_lock into two locks · cecf5d87
      Ming Lei authored 
      The kernfs built-in lock of 'kn->count' is held in sysfs .show/.store
path. Meantime, inside block's .show/.store callback, q->sysfs_lock is
required.

However, when mq & iosched kobjects are removed via
blk_mq_unregister_dev() & elv_unregister_queue(), q->sysfs_lock is held
too. This way causes AB-BA lock because the kernfs built-in lock of
'kn-count' is required inside kobject_del() too, see the lockdep warning[1].

On the other hand, it isn't necessary to acquire q->sysfs_lock for
both blk_mq_unregister_dev() & elv_unregister_queue() because
clearing REGISTERED flag prevents storing to 'queue/scheduler'
from being happened. Also sysfs write(store) is exclusive, so no
necessary to hold the lock for elv_unregister_queue() when it is
called in switching elevator path.

So split .sysfs_lock into two: one is still named as .sysfs_lock for
covering sync .store, the other one is named as .sysfs_dir_lock
for covering kobjects and related status change.

sysfs itself can handle the race between add/remove kobjects and
showing/storing attributes under kobjects. For switching scheduler
via storing to 'queue/scheduler', we use the queue flag of
QUEUE_FLAG_REGISTERED with .sysfs_lock for avoiding the race, then
we can avoid to hold .sysfs_lock during removing/adding kobjects.

[1]  lockdep warning
    ======================================================
    WARNING: possible circular locking dependency detected
    5.3.0-rc3-00044-g73277fc75ea0 #1380 Not tainted
    ------------------------------------------------------
    rmmod/777 is trying to acquire lock:
    00000000ac50e981 (kn->count#202){++++}, at: kernfs_remove_by_name_ns+0x59/0x72

    but task is already holding lock:
    00000000fb16ae21 (&q->sysfs_lock){+.+.}, at: blk_unregister_queue+0x78/0x10b

    which lock already depends on the new lock.

    the existing dependency chain (in reverse order) is:

    -> #1 (&q->sysfs_lock){+.+.}:
           __lock_acquire+0x95f/0xa2f
           lock_acquire+0x1b4/0x1e8
           __mutex_lock+0x14a/0xa9b
           blk_mq_hw_sysfs_show+0x63/0xb6
           sysfs_kf_seq_show+0x11f/0x196
           seq_read+0x2cd/0x5f2
           vfs_read+0xc7/0x18c
           ksys_read+0xc4/0x13e
           do_syscall_64+0xa7/0x295
           entry_SYSCALL_64_after_hwframe+0x49/0xbe

    -> #0 (kn->count#202){++++}:
           check_prev_add+0x5d2/0xc45
           validate_chain+0xed3/0xf94
           __lock_acquire+0x95f/0xa2f
           lock_acquire+0x1b4/0x1e8
           __kernfs_remove+0x237/0x40b
           kernfs_remove_by_name_ns+0x59/0x72
           remove_files+0x61/0x96
           sysfs_remove_group+0x81/0xa4
           sysfs_remove_groups+0x3b/0x44
           kobject_del+0x44/0x94
           blk_mq_unregister_dev+0x83/0xdd
           blk_unregister_queue+0xa0/0x10b
           del_gendisk+0x259/0x3fa
           null_del_dev+0x8b/0x1c3 [null_blk]
           null_exit+0x5c/0x95 [null_blk]
           __se_sys_delete_module+0x204/0x337
           do_syscall_64+0xa7/0x295
           entry_SYSCALL_64_after_hwframe+0x49/0xbe

    other info that might help us debug this:

     Possible unsafe locking scenario:

           CPU0                    CPU1
           ----                    ----
      lock(&q->sysfs_lock);
                                   lock(kn->count#202);
                                   lock(&q->sysfs_lock);
      lock(kn->count#202);

     *** DEADLOCK ***

    2 locks held by rmmod/777:
     #0: 00000000e69bd9de (&lock){+.+.}, at: null_exit+0x2e/0x95 [null_blk]
     #1: 00000000fb16ae21 (&q->sysfs_lock){+.+.}, at: blk_unregister_queue+0x78/0x10b

    stack backtrace:
    CPU: 0 PID: 777 Comm: rmmod Not tainted 5.3.0-rc3-00044-g73277fc75ea0 #1380
    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS ?-20180724_192412-buildhw-07.phx4
    Call Trace:
     dump_stack+0x9a/0xe6
     check_noncircular+0x207/0x251
     ? print_circular_bug+0x32a/0x32a
     ? find_usage_backwards+0x84/0xb0
     check_prev_add+0x5d2/0xc45
     validate_chain+0xed3/0xf94
     ? check_prev_add+0xc45/0xc45
     ? mark_lock+0x11b/0x804
     ? check_usage_forwards+0x1ca/0x1ca
     __lock_acquire+0x95f/0xa2f
     lock_acquire+0x1b4/0x1e8
     ? kernfs_remove_by_name_ns+0x59/0x72
     __kernfs_remove+0x237/0x40b
     ? kernfs_remove_by_name_ns+0x59/0x72
     ? kernfs_next_descendant_post+0x7d/0x7d
     ? strlen+0x10/0x23
     ? strcmp+0x22/0x44
     kernfs_remove_by_name_ns+0x59/0x72
     remove_files+0x61/0x96
     sysfs_remove_group+0x81/0xa4
     sysfs_remove_groups+0x3b/0x44
     kobject_del+0x44/0x94
     blk_mq_unregister_dev+0x83/0xdd
     blk_unregister_queue+0xa0/0x10b
     del_gendisk+0x259/0x3fa
     ? disk_events_poll_msecs_store+0x12b/0x12b
     ? check_flags+0x1ea/0x204
     ? mark_held_locks+0x1f/0x7a
     null_del_dev+0x8b/0x1c3 [null_blk]
     null_exit+0x5c/0x95 [null_blk]
     __se_sys_delete_module+0x204/0x337
     ? free_module+0x39f/0x39f
     ? blkcg_maybe_throttle_current+0x8a/0x718
     ? rwlock_bug+0x62/0x62
     ? __blkcg_punt_bio_submit+0xd0/0xd0
     ? trace_hardirqs_on_thunk+0x1a/0x20
     ? mark_held_locks+0x1f/0x7a
     ? do_syscall_64+0x4c/0x295
     do_syscall_64+0xa7/0x295
     entry_SYSCALL_64_after_hwframe+0x49/0xbe
    RIP: 0033:0x7fb696cdbe6b
    Code: 73 01 c3 48 8b 0d 1d 20 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 008
    RSP: 002b:00007ffec9588788 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
    RAX: ffffffffffffffda RBX: 0000559e589137c0 RCX: 00007fb696cdbe6b
    RDX: 000000000000000a RSI: 0000000000000800 RDI: 0000559e58913828
    RBP: 0000000000000000 R08: 00007ffec9587701 R09: 0000000000000000
    R10: 00007fb696d4eae0 R11: 0000000000000206 R12: 00007ffec95889b0
    R13: 00007ffec95896b3 R14: 0000559e58913260 R15: 0000559e589137c0

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      cecf5d87
    • Ming Lei's avatar
      block: add helper for checking if queue is registered · 58c898ba
      Ming Lei authored 
      There are 4 users which check if queue is registered, so add one helper
to check it.

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      58c898ba
    • Ming Lei's avatar
      blk-mq: don't hold q->sysfs_lock in blk_mq_map_swqueue · c6ba9333
      Ming Lei authored 
      blk_mq_map_swqueue() is called from blk_mq_init_allocated_queue()
and blk_mq_update_nr_hw_queues(). For the former caller, the kobject
isn't exposed to userspace yet. For the latter caller, hctx sysfs entries
and debugfs are un-registered before updating nr_hw_queues.

On the other hand, commit 2f8f1336 ("blk-mq: always free hctx after
request queue is freed") moves freeing hctx into queue's release
handler, so there won't be race with queue release path too.

So don't hold q->sysfs_lock in blk_mq_map_swqueue().

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      c6ba9333
    • Ming Lei's avatar
      block: don't hold q->sysfs_lock in elevator_init_mq · c48dac13
      Ming Lei authored 
      The original comment says:

	q->sysfs_lock must be held to provide mutual exclusion between
	elevator_switch() and here.

Which is simply wrong. elevator_init_mq() is only called from
blk_mq_init_allocated_queue, which is always called before the request
queue is registered via blk_register_queue(), for dm-rq or normal rq
based driver. However, queue's kobject is only exposed and added to sysfs
in blk_register_queue(). So there isn't such race between elevator_switch()
and elevator_init_mq().

So avoid to hold q->sysfs_lock in elevator_init_mq().

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      c48dac13
    • Bart Van Assche's avatar
      block: Remove blk_mq_register_dev() · 9685b227
      Bart Van Assche authored 
      This function has no callers. Hence remove it.

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      9685b227
    • Tejun Heo's avatar
      writeback, memcg: Implement foreign dirty flushing · 97b27821
      Tejun Heo authored 
      There's an inherent mismatch between memcg and writeback.  The former
trackes ownership per-page while the latter per-inode.  This was a
deliberate design decision because honoring per-page ownership in the
writeback path is complicated, may lead to higher CPU and IO overheads
and deemed unnecessary given that write-sharing an inode across
different cgroups isn't a common use-case.

Combined with inode majority-writer ownership switching, this works
well enough in most cases but there are some pathological cases.  For
example, let's say there are two cgroups A and B which keep writing to
different but confined parts of the same inode.  B owns the inode and
A's memory is limited far below B's.  A's dirty ratio can rise enough
to trigger balance_dirty_pages() sleeps but B's can be low enough to
avoid triggering background writeback.  A will be slowed down without
a way to make writeback of the dirty pages happen.

This patch implements foreign dirty recording and foreign mechanism so
that when a memcg encounters a condition as above it can trigger
flushes on bdi_writebacks which can clean its pages.  Please see the
comment on top of mem_cgroup_track_foreign_dirty_slowpath() for
details.

A reproducer follows.

write-range.c::

  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <fcntl.h>
  #include <sys/types.h>

  static const char *usage = "write-range FILE START SIZE\n";

  int main(int argc, char **argv)
  {
	  int fd;
	  unsigned long start, size, end, pos;
	  char *endp;
	  char buf[4096];

	  if (argc < 4) {
		  fprintf(stderr, usage);
		  return 1;
	  }

	  fd = open(argv[1], O_WRONLY);
	  if (fd < 0) {
		  perror("open");
		  return 1;
	  }

	  start = strtoul(argv[2], &endp, 0);
	  if (*endp != '\0') {
		  fprintf(stderr, usage);
		  return 1;
	  }

	  size = strtoul(argv[3], &endp, 0);
	  if (*endp != '\0') {
		  fprintf(stderr, usage);
		  return 1;
	  }

	  end = start + size;

	  while (1) {
		  for (pos = start; pos < end; ) {
			  long bread, bwritten = 0;

			  if (lseek(fd, pos, SEEK_SET) < 0) {
				  perror("lseek");
				  return 1;
			  }

			  bread = read(0, buf, sizeof(buf) < end - pos ?
					       sizeof(buf) : end - pos);
			  if (bread < 0) {
				  perror("read");
				  return 1;
			  }
			  if (bread == 0)
				  return 0;

			  while (bwritten < bread) {
				  long this;

				  this = write(fd, buf + bwritten,
					       bread - bwritten);
				  if (this < 0) {
					  perror("write");
					  return 1;
				  }

				  bwritten += this;
				  pos += bwritten;
			  }
		  }
	  }
  }

repro.sh::

  #!/bin/bash

  set -e
  set -x

  sysctl -w vm.dirty_expire_centisecs=300000
  sysctl -w vm.dirty_writeback_centisecs=300000
  sysctl -w vm.dirtytime_expire_seconds=300000
  echo 3 > /proc/sys/vm/drop_caches

  TEST=/sys/fs/cgroup/test
  A=$TEST/A
  B=$TEST/B

  mkdir -p $A $B
  echo "+memory +io" > $TEST/cgroup.subtree_control
  echo $((1<<30)) > $A/memory.high
  echo $((32<<30)) > $B/memory.high

  rm -f testfile
  touch testfile
  fallocate -l 4G testfile

  echo "Starting B"

  (echo $BASHPID > $B/cgroup.procs
   pv -q --rate-limit 70M < /dev/urandom | ./write-range testfile $((2<<30)) $((2<<30))) &

  echo "Waiting 10s to ensure B claims the testfile inode"
  sleep 5
  sync
  sleep 5
  sync
  echo "Starting A"

  (echo $BASHPID > $A/cgroup.procs
   pv < /dev/urandom | ./write-range testfile 0 $((2<<30)))

v2: Added comments explaining why the specific intervals are being used.

v3: Use 0 @nr when calling cgroup_writeback_by_id() to use best-effort
    flushing while avoding possible livelocks.

v4: Use get_jiffies_64() and time_before/after64() instead of raw
    jiffies_64 and arthimetic comparisons as suggested by Jan.
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      97b27821
    • Tejun Heo's avatar
      writeback, memcg: Implement cgroup_writeback_by_id() · d62241c7
      Tejun Heo authored 
      Implement cgroup_writeback_by_id() which initiates cgroup writeback
from bdi and memcg IDs.  This will be used by memcg foreign inode
flushing.

v2: Use wb_get_lookup() instead of wb_get_create() to avoid creating
    spurious wbs.

v3: Interpret 0 @nr as 1.25 * nr_dirty to implement best-effort
    flushing while avoding possible livelocks.
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      d62241c7
    • Tejun Heo's avatar
      writeback: Separate out wb_get_lookup() from wb_get_create() · ed288dc0
      Tejun Heo authored 
      Separate out wb_get_lookup() which doesn't try to create one if there
isn't already one from wb_get_create().  This will be used by later
patches.
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      ed288dc0
    • Tejun Heo's avatar
      bdi: Add bdi->id · 34f8fe50
      Tejun Heo authored 
      There currently is no way to universally identify and lookup a bdi
without holding a reference and pointer to it.  This patch adds an
non-recycling bdi->id and implements bdi_get_by_id() which looks up
bdis by their ids.  This will be used by memcg foreign inode flushing.

I left bdi_list alone for simplicity and because while rb_tree does
support rcu assignment it doesn't seem to guarantee lossless walk when
walk is racing aginst tree rebalance operations.
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      34f8fe50
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