From: Josef Bacik <jo...@toxicpanda.com>
commit e89c4a9c8e6ce3a84cab4f342687d3fbbb1234eb upstream.
I got the following lockdep splat while testing:
======================================================
WARNING: possible circular locking dependency detected
5.8.0-rc7-00172-g021118712e59 #932 Not tainted
------------------------------------------------------
btrfs/229626 is trying to acquire lock:
ffffffff828513f0 (cpu_hotplug_lock){++++}-{0:0}, at:
alloc_workqueue+0x378/0x450
but task is already holding lock:
ffff889dd3889518 (&fs_info->scrub_lock){+.+.}-{3:3}, at:
btrfs_scrub_dev+0x11c/0x630
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #7 (&fs_info->scrub_lock){+.+.}-{3:3}:
__mutex_lock+0x9f/0x930
btrfs_scrub_dev+0x11c/0x630
btrfs_dev_replace_by_ioctl.cold.21+0x10a/0x1d4
btrfs_ioctl+0x2799/0x30a0
ksys_ioctl+0x83/0xc0
__x64_sys_ioctl+0x16/0x20
do_syscall_64+0x50/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #6 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
__mutex_lock+0x9f/0x930
btrfs_run_dev_stats+0x49/0x480
commit_cowonly_roots+0xb5/0x2a0
btrfs_commit_transaction+0x516/0xa60
sync_filesystem+0x6b/0x90
generic_shutdown_super+0x22/0x100
kill_anon_super+0xe/0x30
btrfs_kill_super+0x12/0x20
deactivate_locked_super+0x29/0x60
cleanup_mnt+0xb8/0x140
task_work_run+0x6d/0xb0
__prepare_exit_to_usermode+0x1cc/0x1e0
do_syscall_64+0x5c/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #5 (&fs_info->tree_log_mutex){+.+.}-{3:3}:
__mutex_lock+0x9f/0x930
btrfs_commit_transaction+0x4bb/0xa60
sync_filesystem+0x6b/0x90
generic_shutdown_super+0x22/0x100
kill_anon_super+0xe/0x30
btrfs_kill_super+0x12/0x20
deactivate_locked_super+0x29/0x60
cleanup_mnt+0xb8/0x140
task_work_run+0x6d/0xb0
__prepare_exit_to_usermode+0x1cc/0x1e0
do_syscall_64+0x5c/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #4 (&fs_info->reloc_mutex){+.+.}-{3:3}:
__mutex_lock+0x9f/0x930
btrfs_record_root_in_trans+0x43/0x70
start_transaction+0xd1/0x5d0
btrfs_dirty_inode+0x42/0xd0
touch_atime+0xa1/0xd0
btrfs_file_mmap+0x3f/0x60
mmap_region+0x3a4/0x640
do_mmap+0x376/0x580
vm_mmap_pgoff+0xd5/0x120
ksys_mmap_pgoff+0x193/0x230
do_syscall_64+0x50/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #3 (&mm->mmap_lock#2){++++}-{3:3}:
__might_fault+0x68/0x90
_copy_to_user+0x1e/0x80
perf_read+0x141/0x2c0
vfs_read+0xad/0x1b0
ksys_read+0x5f/0xe0
do_syscall_64+0x50/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #2 (&cpuctx_mutex){+.+.}-{3:3}:
__mutex_lock+0x9f/0x930
perf_event_init_cpu+0x88/0x150
perf_event_init+0x1db/0x20b
start_kernel+0x3ae/0x53c
secondary_startup_64+0xa4/0xb0
-> #1 (pmus_lock){+.+.}-{3:3}:
__mutex_lock+0x9f/0x930
perf_event_init_cpu+0x4f/0x150
cpuhp_invoke_callback+0xb1/0x900
_cpu_up.constprop.26+0x9f/0x130
cpu_up+0x7b/0xc0
bringup_nonboot_cpus+0x4f/0x60
smp_init+0x26/0x71
kernel_init_freeable+0x110/0x258
kernel_init+0xa/0x103
ret_from_fork+0x1f/0x30
-> #0 (cpu_hotplug_lock){++++}-{0:0}:
__lock_acquire+0x1272/0x2310
lock_acquire+0x9e/0x360
cpus_read_lock+0x39/0xb0
alloc_workqueue+0x378/0x450
__btrfs_alloc_workqueue+0x15d/0x200
btrfs_alloc_workqueue+0x51/0x160
scrub_workers_get+0x5a/0x170
btrfs_scrub_dev+0x18c/0x630
btrfs_dev_replace_by_ioctl.cold.21+0x10a/0x1d4
btrfs_ioctl+0x2799/0x30a0
ksys_ioctl+0x83/0xc0
__x64_sys_ioctl+0x16/0x20
do_syscall_64+0x50/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
other info that might help us debug this:
Chain exists of:
cpu_hotplug_lock --> &fs_devs->device_list_mutex --> &fs_info->scrub_lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&fs_info->scrub_lock);
lock(&fs_devs->device_list_mutex);
lock(&fs_info->scrub_lock);
lock(cpu_hotplug_lock);
*** DEADLOCK ***
2 locks held by btrfs/229626:
#0: ffff88bfe8bb86e0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at:
btrfs_scrub_dev+0xbd/0x630
#1: ffff889dd3889518 (&fs_info->scrub_lock){+.+.}-{3:3}, at:
btrfs_scrub_dev+0x11c/0x630
stack backtrace:
CPU: 15 PID: 229626 Comm: btrfs Kdump: loaded Not tainted
5.8.0-rc7-00172-g021118712e59 #932
Hardware name: Quanta Tioga Pass Single Side 01-0030993006/Tioga Pass Single
Side, BIOS F08_3A18 12/20/2018
Call Trace:
dump_stack+0x78/0xa0
check_noncircular+0x165/0x180
__lock_acquire+0x1272/0x2310
lock_acquire+0x9e/0x360
? alloc_workqueue+0x378/0x450
cpus_read_lock+0x39/0xb0
? alloc_workqueue+0x378/0x450
alloc_workqueue+0x378/0x450
? rcu_read_lock_sched_held+0x52/0x80
__btrfs_alloc_workqueue+0x15d/0x200
btrfs_alloc_workqueue+0x51/0x160
scrub_workers_get+0x5a/0x170
btrfs_scrub_dev+0x18c/0x630
? start_transaction+0xd1/0x5d0
btrfs_dev_replace_by_ioctl.cold.21+0x10a/0x1d4
btrfs_ioctl+0x2799/0x30a0
? do_sigaction+0x102/0x250
? lockdep_hardirqs_on_prepare+0xca/0x160
? _raw_spin_unlock_irq+0x24/0x30
? trace_hardirqs_on+0x1c/0xe0
? _raw_spin_unlock_irq+0x24/0x30
? do_sigaction+0x102/0x250
? ksys_ioctl+0x83/0xc0
ksys_ioctl+0x83/0xc0
__x64_sys_ioctl+0x16/0x20
do_syscall_64+0x50/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
This happens because we're allocating the scrub workqueues under the
scrub and device list mutex, which brings in a whole host of other
dependencies.
Because the work queue allocation is done with GFP_KERNEL, it can
trigger reclaim, which can lead to a transaction commit, which in turns
needs the device_list_mutex, it can lead to a deadlock. A different
problem for which this fix is a solution.
Fix this by moving the actual allocation outside of the
scrub lock, and then only take the lock once we're ready to actually
assign them to the fs_info. We'll now have to cleanup the workqueues in
a few more places, so I've added a helper to do the refcount dance to
safely free the workqueues.
CC: sta...@vger.kernel.org # 5.4+
Reviewed-by: Filipe Manana <fdman...@suse.com>
Signed-off-by: Josef Bacik <jo...@toxicpanda.com>
Reviewed-by: David Sterba <dste...@suse.com>
Signed-off-by: David Sterba <dste...@suse.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
fs/btrfs/scrub.c | 122 +++++++++++++++++++++++++++++++------------------------
1 file changed, 70 insertions(+), 52 deletions(-)
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3742,50 +3742,84 @@ static noinline_for_stack int scrub_supe
return 0;
}
+static void scrub_workers_put(struct btrfs_fs_info *fs_info)
+{
+ if (refcount_dec_and_mutex_lock(&fs_info->scrub_workers_refcnt,
+ &fs_info->scrub_lock)) {
+ struct btrfs_workqueue *scrub_workers = NULL;
+ struct btrfs_workqueue *scrub_wr_comp = NULL;
+ struct btrfs_workqueue *scrub_parity = NULL;
+
+ scrub_workers = fs_info->scrub_workers;
+ scrub_wr_comp = fs_info->scrub_wr_completion_workers;
+ scrub_parity = fs_info->scrub_parity_workers;
+
+ fs_info->scrub_workers = NULL;
+ fs_info->scrub_wr_completion_workers = NULL;
+ fs_info->scrub_parity_workers = NULL;
+ mutex_unlock(&fs_info->scrub_lock);
+
+ btrfs_destroy_workqueue(scrub_workers);
+ btrfs_destroy_workqueue(scrub_wr_comp);
+ btrfs_destroy_workqueue(scrub_parity);
+ }
+}
+
/*
* get a reference count on fs_info->scrub_workers. start worker if necessary
*/
static noinline_for_stack int scrub_workers_get(struct btrfs_fs_info *fs_info,
int is_dev_replace)
{
+ struct btrfs_workqueue *scrub_workers = NULL;
+ struct btrfs_workqueue *scrub_wr_comp = NULL;
+ struct btrfs_workqueue *scrub_parity = NULL;
unsigned int flags = WQ_FREEZABLE | WQ_UNBOUND;
int max_active = fs_info->thread_pool_size;
+ int ret = -ENOMEM;
- lockdep_assert_held(&fs_info->scrub_lock);
+ if (refcount_inc_not_zero(&fs_info->scrub_workers_refcnt))
+ return 0;
- if (refcount_read(&fs_info->scrub_workers_refcnt) == 0) {
- ASSERT(fs_info->scrub_workers == NULL);
- fs_info->scrub_workers = btrfs_alloc_workqueue(fs_info, "scrub",
- flags, is_dev_replace ? 1 : max_active, 4);
- if (!fs_info->scrub_workers)
- goto fail_scrub_workers;
-
- ASSERT(fs_info->scrub_wr_completion_workers == NULL);
- fs_info->scrub_wr_completion_workers =
- btrfs_alloc_workqueue(fs_info, "scrubwrc", flags,
- max_active, 2);
- if (!fs_info->scrub_wr_completion_workers)
- goto fail_scrub_wr_completion_workers;
+ scrub_workers = btrfs_alloc_workqueue(fs_info, "scrub", flags,
+ is_dev_replace ? 1 : max_active,
4);
+ if (!scrub_workers)
+ goto fail_scrub_workers;
- ASSERT(fs_info->scrub_parity_workers == NULL);
- fs_info->scrub_parity_workers =
- btrfs_alloc_workqueue(fs_info, "scrubparity", flags,
+ scrub_wr_comp = btrfs_alloc_workqueue(fs_info, "scrubwrc", flags,
max_active, 2);
- if (!fs_info->scrub_parity_workers)
- goto fail_scrub_parity_workers;
+ if (!scrub_wr_comp)
+ goto fail_scrub_wr_completion_workers;
+ scrub_parity = btrfs_alloc_workqueue(fs_info, "scrubparity", flags,
+ max_active, 2);
+ if (!scrub_parity)
+ goto fail_scrub_parity_workers;
+
+ mutex_lock(&fs_info->scrub_lock);
+ if (refcount_read(&fs_info->scrub_workers_refcnt) == 0) {
+ ASSERT(fs_info->scrub_workers == NULL &&
+ fs_info->scrub_wr_completion_workers == NULL &&
+ fs_info->scrub_parity_workers == NULL);
+ fs_info->scrub_workers = scrub_workers;
+ fs_info->scrub_wr_completion_workers = scrub_wr_comp;
+ fs_info->scrub_parity_workers = scrub_parity;
refcount_set(&fs_info->scrub_workers_refcnt, 1);
- } else {
- refcount_inc(&fs_info->scrub_workers_refcnt);
+ mutex_unlock(&fs_info->scrub_lock);
+ return 0;
}
- return 0;
+ /* Other thread raced in and created the workers for us */
+ refcount_inc(&fs_info->scrub_workers_refcnt);
+ mutex_unlock(&fs_info->scrub_lock);
+ ret = 0;
+ btrfs_destroy_workqueue(scrub_parity);
fail_scrub_parity_workers:
- btrfs_destroy_workqueue(fs_info->scrub_wr_completion_workers);
+ btrfs_destroy_workqueue(scrub_wr_comp);
fail_scrub_wr_completion_workers:
- btrfs_destroy_workqueue(fs_info->scrub_workers);
+ btrfs_destroy_workqueue(scrub_workers);
fail_scrub_workers:
- return -ENOMEM;
+ return ret;
}
int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
@@ -3796,9 +3830,6 @@ int btrfs_scrub_dev(struct btrfs_fs_info
int ret;
struct btrfs_device *dev;
unsigned int nofs_flag;
- struct btrfs_workqueue *scrub_workers = NULL;
- struct btrfs_workqueue *scrub_wr_comp = NULL;
- struct btrfs_workqueue *scrub_parity = NULL;
if (btrfs_fs_closing(fs_info))
return -EAGAIN;
@@ -3845,13 +3876,17 @@ int btrfs_scrub_dev(struct btrfs_fs_info
if (IS_ERR(sctx))
return PTR_ERR(sctx);
+ ret = scrub_workers_get(fs_info, is_dev_replace);
+ if (ret)
+ goto out_free_ctx;
+
mutex_lock(&fs_info->fs_devices->device_list_mutex);
dev = btrfs_find_device(fs_info->fs_devices, devid, NULL, NULL, true);
if (!dev || (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state) &&
!is_dev_replace)) {
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
ret = -ENODEV;
- goto out_free_ctx;
+ goto out;
}
if (!is_dev_replace && !readonly &&
@@ -3860,7 +3895,7 @@ int btrfs_scrub_dev(struct btrfs_fs_info
btrfs_err_in_rcu(fs_info, "scrub: device %s is not writable",
rcu_str_deref(dev->name));
ret = -EROFS;
- goto out_free_ctx;
+ goto out;
}
mutex_lock(&fs_info->scrub_lock);
@@ -3869,7 +3904,7 @@ int btrfs_scrub_dev(struct btrfs_fs_info
mutex_unlock(&fs_info->scrub_lock);
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
ret = -EIO;
- goto out_free_ctx;
+ goto out;
}
down_read(&fs_info->dev_replace.rwsem);
@@ -3880,17 +3915,10 @@ int btrfs_scrub_dev(struct btrfs_fs_info
mutex_unlock(&fs_info->scrub_lock);
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
ret = -EINPROGRESS;
- goto out_free_ctx;
+ goto out;
}
up_read(&fs_info->dev_replace.rwsem);
- ret = scrub_workers_get(fs_info, is_dev_replace);
- if (ret) {
- mutex_unlock(&fs_info->scrub_lock);
- mutex_unlock(&fs_info->fs_devices->device_list_mutex);
- goto out_free_ctx;
- }
-
sctx->readonly = readonly;
dev->scrub_ctx = sctx;
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
@@ -3943,24 +3971,14 @@ int btrfs_scrub_dev(struct btrfs_fs_info
mutex_lock(&fs_info->scrub_lock);
dev->scrub_ctx = NULL;
- if (refcount_dec_and_test(&fs_info->scrub_workers_refcnt)) {
- scrub_workers = fs_info->scrub_workers;
- scrub_wr_comp = fs_info->scrub_wr_completion_workers;
- scrub_parity = fs_info->scrub_parity_workers;
-
- fs_info->scrub_workers = NULL;
- fs_info->scrub_wr_completion_workers = NULL;
- fs_info->scrub_parity_workers = NULL;
- }
mutex_unlock(&fs_info->scrub_lock);
- btrfs_destroy_workqueue(scrub_workers);
- btrfs_destroy_workqueue(scrub_wr_comp);
- btrfs_destroy_workqueue(scrub_parity);
+ scrub_workers_put(fs_info);
scrub_put_ctx(sctx);
return ret;
-
+out:
+ scrub_workers_put(fs_info);
out_free_ctx:
scrub_free_ctx(sctx);
