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Date: Mon, 16 Oct 2017 20:06:28 +0900 From: Byungchul Park <byungchul.park@....com> To: Peter Zijlstra <peterz@...radead.org>, david@...morbit.com, darrick.wong@...cle.com Cc: Tejun Heo <tj@...nel.org>, johannes.berg@...el.com, mingo@...nel.org, tglx@...utronix.de, oleg@...hat.com, linux-kernel@...r.kernel.org, kernel-team@....com Subject: Re: [RESEND PATCH v2 2/2] lockdep: Remove unnecessary acquisitions wrt workqueue flush On Mon, Oct 16, 2017 at 07:58:57PM +0900, Byungchul Park wrote: > On Fri, Oct 13, 2017 at 10:27:50AM +0200, Peter Zijlstra wrote: > > On Fri, Oct 13, 2017 at 04:56:33PM +0900, Byungchul Park wrote: > > > On Thu, Oct 12, 2017 at 05:56:35PM +0200, Peter Zijlstra wrote: > > > > On Thu, Oct 12, 2017 at 08:38:17AM -0700, Tejun Heo wrote: > > > > > > > > > > As long as we have the same level of protection, simpler code is of > > > > > course preferable. That said, I haven't followed the discussion > > > > > closely and don't want to apply it without Peter's ack. Peter? > > > > > > > > I'm really tied up atm; and feel we should be addressing the false > > > > positives generated by the current code before we start doing new stuff > > > > on top. > > > > > > We can never avoid adding false dependencies as long as we use > > > acquisitions in that way the workqueue code does, even though you > > > successfully replace write acquisitions with recursive-read ones after > > > making them work, as you know. > > > > Not the point; they still need to get annotated away. The block layer > > and xfs are now fairly consistently triggering lockdep splats, that > > needs to get sorted. > > I believe that the following patch is helpful for that issue. Could you > check if it works, and give your opinion? I will add more comments on it > if you let me know if this patch is acceptable. I missed something to tell you, the following patch should be applied on top of the first patch of this patchset, "completion: Add support for initializing completion with lockdep_map". > ----->8----- > >From 340846e59c28457faf4d8051fb0c8a4c9da8c9b1 Mon Sep 17 00:00:00 2001 > From: Byungchul Park <byungchul.park@....com> > Date: Mon, 16 Oct 2017 18:51:51 +0900 > Subject: [RFC] lockdep: Assign a lock_class per gendisk used for > wait_for_completion() > > Darrick and Dave Chinner posted the following warning: > > > ====================================================== > > WARNING: possible circular locking dependency detected > > 4.14.0-rc1-fixes #1 Tainted: G W > > ------------------------------------------------------ > > loop0/31693 is trying to acquire lock: > > (&(&ip->i_mmaplock)->mr_lock){++++}, at: [<ffffffffa00f1b0c>] xfs_ilock+0x23c/0x330 [xfs] > > > > but now in release context of a crosslock acquired at the following: > > ((complete)&ret.event){+.+.}, at: [<ffffffff81326c1f>] submit_bio_wait+0x7f/0xb0 > > > > which lock already depends on the new lock. > > > > the existing dependency chain (in reverse order) is: > > > > -> #2 ((complete)&ret.event){+.+.}: > > lock_acquire+0xab/0x200 > > wait_for_completion_io+0x4e/0x1a0 > > submit_bio_wait+0x7f/0xb0 > > blkdev_issue_zeroout+0x71/0xa0 > > xfs_bmapi_convert_unwritten+0x11f/0x1d0 [xfs] > > xfs_bmapi_write+0x374/0x11f0 [xfs] > > xfs_iomap_write_direct+0x2ac/0x430 [xfs] > > xfs_file_iomap_begin+0x20d/0xd50 [xfs] > > iomap_apply+0x43/0xe0 > > dax_iomap_rw+0x89/0xf0 > > xfs_file_dax_write+0xcc/0x220 [xfs] > > xfs_file_write_iter+0xf0/0x130 [xfs] > > __vfs_write+0xd9/0x150 > > vfs_write+0xc8/0x1c0 > > SyS_write+0x45/0xa0 > > entry_SYSCALL_64_fastpath+0x1f/0xbe > > > > -> #1 (&xfs_nondir_ilock_class){++++}: > > lock_acquire+0xab/0x200 > > down_write_nested+0x4a/0xb0 > > xfs_ilock+0x263/0x330 [xfs] > > xfs_setattr_size+0x152/0x370 [xfs] > > xfs_vn_setattr+0x6b/0x90 [xfs] > > notify_change+0x27d/0x3f0 > > do_truncate+0x5b/0x90 > > path_openat+0x237/0xa90 > > do_filp_open+0x8a/0xf0 > > do_sys_open+0x11c/0x1f0 > > entry_SYSCALL_64_fastpath+0x1f/0xbe > > > > -> #0 (&(&ip->i_mmaplock)->mr_lock){++++}: > > up_write+0x1c/0x40 > > xfs_iunlock+0x1d0/0x310 [xfs] > > xfs_file_fallocate+0x8a/0x310 [xfs] > > loop_queue_work+0xb7/0x8d0 > > kthread_worker_fn+0xb9/0x1f0 > > > > Chain exists of: > > &(&ip->i_mmaplock)->mr_lock --> &xfs_nondir_ilock_class --> (complete)&ret.event > > > > Possible unsafe locking scenario by crosslock: > > > > CPU0 CPU1 > > ---- ---- > > lock(&xfs_nondir_ilock_class); > > lock((complete)&ret.event); > > lock(&(&ip->i_mmaplock)->mr_lock); > > unlock((complete)&ret.event); > > > > *** DEADLOCK *** > > The warning is a false positive, caused by the fact that all > wait_for_completion()s in submit_bio_wait() are waiting with the same > lock class. > > However, some bios have nothing to do with others, for example, the case > might happen while using loop devices, between bios of an upper device > and a lower device(=loop device). > > The safest way to assign different lock classes to different devices is > to do it for each gendisk. In other words, this patch assigns a > lockdep_map per gendisk and uses it when initializing completion in > submit_bio_wait(). > > Of course, it might be too conservative. But, making it safest for now > and extended by block layer experts later is good, atm. > > Signed-off-by: Byungchul Park <byungchul.park@....com> > --- > block/bio.c | 4 ++-- > block/genhd.c | 13 +++++-------- > include/linux/genhd.h | 26 ++++++++++++++++++++++---- > 3 files changed, 29 insertions(+), 14 deletions(-) > > diff --git a/block/bio.c b/block/bio.c > index 9a63597..0d4d6c0 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -941,7 +941,7 @@ int submit_bio_wait(struct bio *bio) > { > struct submit_bio_ret ret; > > - init_completion(&ret.event); > + init_completion_with_map(&ret.event, &bio->bi_disk->lockdep_map); > bio->bi_private = &ret; > bio->bi_end_io = submit_bio_wait_endio; > bio->bi_opf |= REQ_SYNC; > @@ -1382,7 +1382,7 @@ struct bio *bio_map_user_iov(struct request_queue *q, > > if (len <= 0) > break; > - > + > if (bytes > len) > bytes = len; > > diff --git a/block/genhd.c b/block/genhd.c > index 7f520fa..676c245 100644 > --- a/block/genhd.c > +++ b/block/genhd.c > @@ -1304,13 +1304,7 @@ dev_t blk_lookup_devt(const char *name, int partno) > } > EXPORT_SYMBOL(blk_lookup_devt); > > -struct gendisk *alloc_disk(int minors) > -{ > - return alloc_disk_node(minors, NUMA_NO_NODE); > -} > -EXPORT_SYMBOL(alloc_disk); > - > -struct gendisk *alloc_disk_node(int minors, int node_id) > +struct gendisk *__alloc_disk_node(int minors, int node_id, struct lock_class_key *key, const char *lock_name) > { > struct gendisk *disk; > > @@ -1350,9 +1344,12 @@ struct gendisk *alloc_disk_node(int minors, int node_id) > disk_to_dev(disk)->type = &disk_type; > device_initialize(disk_to_dev(disk)); > } > + > + lockdep_init_map(&disk->lockdep_map, lock_name, key, 0); > + > return disk; > } > -EXPORT_SYMBOL(alloc_disk_node); > +EXPORT_SYMBOL(__alloc_disk_node); > > struct kobject *get_disk(struct gendisk *disk) > { > diff --git a/include/linux/genhd.h b/include/linux/genhd.h > index e619fae..5225efc 100644 > --- a/include/linux/genhd.h > +++ b/include/linux/genhd.h > @@ -3,7 +3,7 @@ > > /* > * genhd.h Copyright (C) 1992 Drew Eckhardt > - * Generic hard disk header file by > + * Generic hard disk header file by > * Drew Eckhardt > * > * <drew@...orado.edu> > @@ -206,6 +206,9 @@ struct gendisk { > #endif /* CONFIG_BLK_DEV_INTEGRITY */ > int node_id; > struct badblocks *bb; > +#ifdef CONFIG_LOCKDEP_COMPLETIONS > + struct lockdep_map lockdep_map; > +#endif > }; > > static inline struct gendisk *part_to_disk(struct hd_struct *part) > @@ -483,7 +486,7 @@ struct bsd_disklabel { > __s16 d_type; /* drive type */ > __s16 d_subtype; /* controller/d_type specific */ > char d_typename[16]; /* type name, e.g. "eagle" */ > - char d_packname[16]; /* pack identifier */ > + char d_packname[16]; /* pack identifier */ > __u32 d_secsize; /* # of bytes per sector */ > __u32 d_nsectors; /* # of data sectors per track */ > __u32 d_ntracks; /* # of tracks per cylinder */ > @@ -602,8 +605,7 @@ extern struct hd_struct * __must_check add_partition(struct gendisk *disk, > extern void delete_partition(struct gendisk *, int); > extern void printk_all_partitions(void); > > -extern struct gendisk *alloc_disk_node(int minors, int node_id); > -extern struct gendisk *alloc_disk(int minors); > +extern struct gendisk *__alloc_disk_node(int minors, int node_id, struct lock_class_key *key, const char *lock_name); > extern struct kobject *get_disk(struct gendisk *disk); > extern void put_disk(struct gendisk *disk); > extern void blk_register_region(dev_t devt, unsigned long range, > @@ -627,6 +629,22 @@ extern ssize_t part_fail_store(struct device *dev, > const char *buf, size_t count); > #endif /* CONFIG_FAIL_MAKE_REQUEST */ > > +#ifdef CONFIG_LOCKDEP_COMPLETIONS > +#define alloc_disk_node(m, id) \ > +({ \ > + static struct lock_class_key __key; \ > + const char *__lock_name; \ > + \ > + __lock_name = "(complete)"#m"("#id")"; \ > + \ > + __alloc_disk_node(m, id, &__key, __lock_name); \ > +}) > +#else > +#define alloc_disk_node(m, id) __alloc_disk_node(m, id, NULL, NULL) > +#endif > + > +#define alloc_disk(m) alloc_disk_node(m, NUMA_NO_NODE) > + > static inline int hd_ref_init(struct hd_struct *part) > { > if (percpu_ref_init(&part->ref, __delete_partition, 0, > -- > 1.9.1
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