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Bart Van Assche 669de8bda8 kernel/workqueue: Use dynamic lockdep keys for workqueues 
The following commit:

  87915adc3f ("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 patch
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:
  00000000a01cfe1a ((wq_completion)"dio/%s"sb->s_id){+.+.}, at: flush_workqueue+0xd0/0x970

  but task is already holding lock:
  00000000a0acecf9 (&sb->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 (&sb->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)(&dio->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)(&dio->complete_work) --> &sb->s_type->i_mutex_key#14

   Possible unsafe locking scenario:

         CPU0                    CPU1
         ----                    ----
    lock(&sb->s_type->i_mutex_key#14);
                                 lock((work_completion)(&dio->complete_work));
                                 lock(&sb->s_type->i_mutex_key#14);
    lock((wq_completion)"dio/%s"sb->s_id);

   *** DEADLOCK ***

  1 lock held by fio/4129:
   #0: 00000000a0acecf9 (&sb->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

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190214230058.196511-20-bvanassche@acm.org
[ Reworked the changelog a bit. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-02-28 07:55:47 +01:00
arch Merge branch 'linus' into locking/core, to pick up fixes 2019-02-28 07:50:39 +01:00
block for-linus-20190215 2019-02-15 09:12:28 -08:00
certs kbuild: remove redundant target cleaning on failure 2019-01-06 09:46:51 +09:00
crypto net: crypto set sk to NULL when af_alg_release. 2019-02-18 12:01:24 -08:00
Documentation Merge branch 'linus' into locking/core, to pick up fixes 2019-02-28 07:50:39 +01:00
drivers Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
firmware kbuild: change filechk to surround the given command with { } 2019-01-06 09:46:51 +09:00
fs locking/percpu-rwsem: Remove preempt_disable variants 2019-02-28 07:55:37 +01:00
include kernel/workqueue: Use dynamic lockdep keys for workqueues 2019-02-28 07:55:47 +01:00
init revert "initramfs: cleanup incomplete rootfs" 2019-02-21 09:00:59 -08:00
ipc ipc: IPCMNI limit check for semmni 2018-10-31 08:54:14 -07:00
kernel kernel/workqueue: Use dynamic lockdep keys for workqueues 2019-02-28 07:55:47 +01:00
lib locking/lockdep: Make it easy to detect whether or not inside a selftest 2019-02-28 07:55:43 +01:00
LICENSES This is a fairly typical cycle for documentation. There's some welcome 2018-10-24 18:01:11 +01:00
mm tmpfs: fix uninitialized return value in shmem_link 2019-02-25 11:49:22 -08:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
samples samples: mei: use /dev/mei0 instead of /dev/mei 2019-01-30 15:24:45 +01:00
scripts Merge branch 'linus' into locking/core, to pick up fixes 2019-02-28 07:50:39 +01:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
sound sound fixes for 5.0 2019-02-20 09:42:52 -08:00
tools Merge branch 'linus' into locking/core, to pick up fixes 2019-02-28 07:50:39 +01:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt KVM/ARM fixes for 5.0: 2019-02-13 19:39:24 +01:00
.clang-format clang-format: Update .clang-format with the latest for_each macro list 2019-01-19 19:26:06 +01:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore kbuild: Add support for DT binding schema checks 2018-12-13 09:41:32 -06:00
.mailmap A few early MIPS fixes for 4.21: 2019-01-05 12:48:25 -08:00
COPYING
CREDITS CREDITS/MAINTAINERS: Retire parisc-linux.org email domain 2019-02-21 20:16:10 +01:00
Kbuild Merge branch 'locking/atomics' into locking/core, to pick up WIP commits 2019-02-11 14:27:05 +01:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge branch 'linus' into locking/core, to pick up fixes 2019-02-28 07:50:39 +01:00
Makefile Linux 5.0-rc8 2019-02-24 16:46:45 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.