[PATCH 2/2] kernel/workqueue: Use dynamic lockdep keys for workqueues
Commit 87915adc3f0a ("workqueue: re-add lockdep dependencies for flushing")
improved deadlock checking in the workqueue implementation. Unfortunately
that patch also introduced a few false positive lockdep complaints. This
patch suppresses these false positives by allocating the workqueue mutex
lockdep key dynamically. An example of a false positive lockdep complaint
suppressed by this report can be found below. The root cause of the
lockdep complaint shown below is that the direct I/O code can call
alloc_workqueue() from inside a work item created by another
alloc_workqueue() call and that both workqueues share the same lockdep
key. This patch avoids that that lockdep complaint is triggered by
allocating the work queue lockdep keys dynamically. In other words, this
patch guarantees that a unique lockdep key is associated with each work
queue mutex.
==
WARNING: possible circular locking dependency detected
4.19.0-dbg+ #1 Not tainted
--
fio/4129 is trying to acquire lock:
a01cfe1a ((wq_completion)"dio/%s"sb->s_id){+.+.}, at:
flush_workqueue+0xd0/0x970
but task is already holding lock:
a0acecf9 (>s_type->i_mutex_key#14){+.+.}, at:
ext4_file_write_iter+0x154/0x710
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (>s_type->i_mutex_key#14){+.+.}:
down_write+0x3d/0x80
__generic_file_fsync+0x77/0xf0
ext4_sync_file+0x3c9/0x780
vfs_fsync_range+0x66/0x100
dio_complete+0x2f5/0x360
dio_aio_complete_work+0x1c/0x20
process_one_work+0x481/0x9f0
worker_thread+0x63/0x5a0
kthread+0x1cf/0x1f0
ret_from_fork+0x24/0x30
-> #1 ((work_completion)(>complete_work)){+.+.}:
process_one_work+0x447/0x9f0
worker_thread+0x63/0x5a0
kthread+0x1cf/0x1f0
ret_from_fork+0x24/0x30
-> #0 ((wq_completion)"dio/%s"sb->s_id){+.+.}:
lock_acquire+0xc5/0x200
flush_workqueue+0xf3/0x970
drain_workqueue+0xec/0x220
destroy_workqueue+0x23/0x350
sb_init_dio_done_wq+0x6a/0x80
do_blockdev_direct_IO+0x1f33/0x4be0
__blockdev_direct_IO+0x79/0x86
ext4_direct_IO+0x5df/0xbb0
generic_file_direct_write+0x119/0x220
__generic_file_write_iter+0x131/0x2d0
ext4_file_write_iter+0x3fa/0x710
aio_write+0x235/0x330
io_submit_one+0x510/0xeb0
__x64_sys_io_submit+0x122/0x340
do_syscall_64+0x71/0x220
entry_SYSCALL_64_after_hwframe+0x49/0xbe
other info that might help us debug this:
Chain exists of:
(wq_completion)"dio/%s"sb->s_id --> (work_completion)(>complete_work)
--> >s_type->i_mutex_key#14
Possible unsafe locking scenario:
CPU0CPU1
lock(>s_type->i_mutex_key#14);
lock((work_completion)(>complete_work));
lock(>s_type->i_mutex_key#14);
lock((wq_completion)"dio/%s"sb->s_id);
*** DEADLOCK ***
1 lock held by fio/4129:
#0: a0acecf9 (>s_type->i_mutex_key#14){+.+.}, at:
ext4_file_write_iter+0x154/0x710
stack backtrace:
CPU: 3 PID: 4129 Comm: fio Not tainted 4.19.0-dbg+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
Call Trace:
dump_stack+0x86/0xc5
print_circular_bug.isra.32+0x20a/0x218
__lock_acquire+0x1c68/0x1cf0
lock_acquire+0xc5/0x200
flush_workqueue+0xf3/0x970
drain_workqueue+0xec/0x220
destroy_workqueue+0x23/0x350
sb_init_dio_done_wq+0x6a/0x80
do_blockdev_direct_IO+0x1f33/0x4be0
__blockdev_direct_IO+0x79/0x86
ext4_direct_IO+0x5df/0xbb0
generic_file_direct_write+0x119/0x220
__generic_file_write_iter+0x131/0x2d0
ext4_file_write_iter+0x3fa/0x710
aio_write+0x235/0x330
io_submit_one+0x510/0xeb0
__x64_sys_io_submit+0x122/0x340
do_syscall_64+0x71/0x220
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Cc: Peter Zijlstra
Cc: Ingo Molnar
Cc: Will Deacon
Cc: Tejun Heo
Cc: Johannes Berg
Signed-off-by: Bart Van Assche
---
include/linux/workqueue.h | 28 ---
kernel/workqueue.c| 48 ---
2 files changed, 44 insertions(+), 32 deletions(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 60d673e15632..d9a1a480e920 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -390,43 +390,23 @@ extern struct workqueue_struct *system_freezable_wq;
extern struct workqueue_struct *system_power_efficient_wq;
extern struct workqueue_struct *system_freezable_power_efficient_wq;
-extern struct workqueue_struct *
-__alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
- struct lock_class_key *key, const char *lock_name, ...) __printf(1, 6);
-
/**
* alloc_workqueue - allocate a workqueue
* @fmt: printf format for the name of the workqueue
* @flags: WQ_* flags
* @max_active: max
[PATCH 2/2] kernel/workqueue: Use dynamic lockdep keys for workqueues
Commit 87915adc3f0a ("workqueue: re-add lockdep dependencies for flushing")
improved deadlock checking in the workqueue implementation. Unfortunately
that patch also introduced a few false positive lockdep complaints. This
patch suppresses these false positives by allocating the workqueue mutex
lockdep key dynamically. An example of a false positive lockdep complaint
suppressed by this report can be found below. The root cause of the
lockdep complaint shown below is that the direct I/O code can call
alloc_workqueue() from inside a work item created by another
alloc_workqueue() call and that both workqueues share the same lockdep
key. This patch avoids that that lockdep complaint is triggered by
allocating the work queue lockdep keys dynamically. In other words, this
patch guarantees that a unique lockdep key is associated with each work
queue mutex.
==
WARNING: possible circular locking dependency detected
4.19.0-dbg+ #1 Not tainted
--
fio/4129 is trying to acquire lock:
a01cfe1a ((wq_completion)"dio/%s"sb->s_id){+.+.}, at:
flush_workqueue+0xd0/0x970
but task is already holding lock:
a0acecf9 (>s_type->i_mutex_key#14){+.+.}, at:
ext4_file_write_iter+0x154/0x710
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (>s_type->i_mutex_key#14){+.+.}:
down_write+0x3d/0x80
__generic_file_fsync+0x77/0xf0
ext4_sync_file+0x3c9/0x780
vfs_fsync_range+0x66/0x100
dio_complete+0x2f5/0x360
dio_aio_complete_work+0x1c/0x20
process_one_work+0x481/0x9f0
worker_thread+0x63/0x5a0
kthread+0x1cf/0x1f0
ret_from_fork+0x24/0x30
-> #1 ((work_completion)(>complete_work)){+.+.}:
process_one_work+0x447/0x9f0
worker_thread+0x63/0x5a0
kthread+0x1cf/0x1f0
ret_from_fork+0x24/0x30
-> #0 ((wq_completion)"dio/%s"sb->s_id){+.+.}:
lock_acquire+0xc5/0x200
flush_workqueue+0xf3/0x970
drain_workqueue+0xec/0x220
destroy_workqueue+0x23/0x350
sb_init_dio_done_wq+0x6a/0x80
do_blockdev_direct_IO+0x1f33/0x4be0
__blockdev_direct_IO+0x79/0x86
ext4_direct_IO+0x5df/0xbb0
generic_file_direct_write+0x119/0x220
__generic_file_write_iter+0x131/0x2d0
ext4_file_write_iter+0x3fa/0x710
aio_write+0x235/0x330
io_submit_one+0x510/0xeb0
__x64_sys_io_submit+0x122/0x340
do_syscall_64+0x71/0x220
entry_SYSCALL_64_after_hwframe+0x49/0xbe
other info that might help us debug this:
Chain exists of:
(wq_completion)"dio/%s"sb->s_id --> (work_completion)(>complete_work)
--> >s_type->i_mutex_key#14
Possible unsafe locking scenario:
CPU0CPU1
lock(>s_type->i_mutex_key#14);
lock((work_completion)(>complete_work));
lock(>s_type->i_mutex_key#14);
lock((wq_completion)"dio/%s"sb->s_id);
*** DEADLOCK ***
1 lock held by fio/4129:
#0: a0acecf9 (>s_type->i_mutex_key#14){+.+.}, at:
ext4_file_write_iter+0x154/0x710
stack backtrace:
CPU: 3 PID: 4129 Comm: fio Not tainted 4.19.0-dbg+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
Call Trace:
dump_stack+0x86/0xc5
print_circular_bug.isra.32+0x20a/0x218
__lock_acquire+0x1c68/0x1cf0
lock_acquire+0xc5/0x200
flush_workqueue+0xf3/0x970
drain_workqueue+0xec/0x220
destroy_workqueue+0x23/0x350
sb_init_dio_done_wq+0x6a/0x80
do_blockdev_direct_IO+0x1f33/0x4be0
__blockdev_direct_IO+0x79/0x86
ext4_direct_IO+0x5df/0xbb0
generic_file_direct_write+0x119/0x220
__generic_file_write_iter+0x131/0x2d0
ext4_file_write_iter+0x3fa/0x710
aio_write+0x235/0x330
io_submit_one+0x510/0xeb0
__x64_sys_io_submit+0x122/0x340
do_syscall_64+0x71/0x220
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Cc: Peter Zijlstra
Cc: Ingo Molnar
Cc: Will Deacon
Cc: Tejun Heo
Cc: Johannes Berg
Signed-off-by: Bart Van Assche
---
include/linux/workqueue.h | 28 ---
kernel/workqueue.c| 48 ---
2 files changed, 44 insertions(+), 32 deletions(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 60d673e15632..d9a1a480e920 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -390,43 +390,23 @@ extern struct workqueue_struct *system_freezable_wq;
extern struct workqueue_struct *system_power_efficient_wq;
extern struct workqueue_struct *system_freezable_power_efficient_wq;
-extern struct workqueue_struct *
-__alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
- struct lock_class_key *key, const char *lock_name, ...) __printf(1, 6);
-
/**
* alloc_workqueue - allocate a workqueue
* @fmt: printf format for the name of the workqueue
* @flags: WQ_* flags
* @max_active: max
