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SubjectRe: [v8, 11/18] mm, dax: enable filesystems to trigger dev_pagemap ->page_free callbacks
On Wed, Apr 04, 2018 at 02:23:40PM -0700, Andrei Vagin wrote:
> Hi Dan,
>
> I catch the following bug on the linux-next 20180404. git bisect brought me to this commit:


The next patch fixes the problem:

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 5b13da127982..a67a7fe75fd5 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -228,6 +228,10 @@ static void __fs_dax_release(struct dax_device *dax_dev, void *owner)

void fs_dax_release(struct dax_device *dax_dev, void *owner)
{
+ if (!dax_dev) {
+ printk("%s:%d: dax_dev == NULL\n", __func__, __LINE__);
+ return;
+ }
if (dax_dev->ops->fs_release)
dax_dev->ops->fs_release(dax_dev, owner);
else

And here is dmesg from my test vm:
[root@fc24 ~]# dmesg | grep -A 2 -B 2 dax
[ 14.659318] md: Skipping autodetection of RAID arrays. (raid=autodetect will force)
[ 14.662436] EXT4-fs (vda2): couldn't mount as ext3 due to feature incompatibilities
[ 14.663983] fs_dax_release:232: dax_dev == NULL
[ 14.665646] EXT4-fs (vda2): couldn't mount as ext2 due to feature incompatibilities
[ 14.667047] fs_dax_release:232: dax_dev == NULL
[ 14.668933] EXT4-fs (vda2): INFO: recovery required on readonly filesystem
[ 14.670039] EXT4-fs (vda2): write access will be enabled during recovery
>
> commit 8e4d1ccc5286d2c3da6515b92323a3529aa64496 (HEAD, refs/bisect/bad)
> Author: Dan Williams <dan.j.williams@intel.com>
> Date: Sat Oct 21 14:41:13 2017 -0700
>
> mm, dax: enable filesystems to trigger dev_pagemap ->page_free callbacks
>
>
> [ 11.278768] BUG: unable to handle kernel NULL pointer dereference at 0000000000000440
> [ 11.279999] IP: fs_dax_release+0x5/0x90
> [ 11.280587] PGD 0 P4D 0
> [ 11.280973] Oops: 0000 [#1] SMP PTI
> [ 11.281500] Modules linked in:
> [ 11.281968] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.16.0-rc4-00193-g8e4d1ccc5286 #7
> [ 11.283163] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1.fc26 04/01/2014
> [ 11.284418] RIP: 0010:fs_dax_release+0x5/0x90
> [ 11.285068] RSP: 0000:ffffb1480062fbd8 EFLAGS: 00010287
> [ 11.285845] RAX: 0000000000000001 RBX: ffff9e2cb823c088 RCX: 0000000000000003
> [ 11.286896] RDX: 0000000000000000 RSI: ffff9e2cb823c088 RDI: 0000000000000000
> [ 11.287980] RBP: ffffb1480062fcd8 R08: 0000000000000001 R09: 0000000000000000
> [ 11.289147] R10: ffffb1480062fb20 R11: 0000000000000000 R12: 00000000ffffffea
> [ 11.290576] R13: 0000000000000000 R14: 0000000000000000 R15: ffff9e2cb823a048
> [ 11.291630] FS: 0000000000000000(0000) GS:ffff9e2cbfd00000(0000) knlGS:0000000000000000
> [ 11.292781] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 11.293602] CR2: 0000000000000440 CR3: 000000007d21e001 CR4: 00000000003606e0
> [ 11.294817] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 11.296827] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [ 11.298293] Call Trace:
> [ 11.298728] ext4_fill_super+0x31b/0x39d0
> [ 11.299441] ? sget_userns+0x155/0x500
> [ 11.300144] ? vsnprintf+0x253/0x4b0
> [ 11.301223] ? ext4_calculate_overhead+0x4a0/0x4a0
> [ 11.301801] ? snprintf+0x45/0x70
> [ 11.302214] ? ext4_calculate_overhead+0x4a0/0x4a0
> [ 11.302822] mount_bdev+0x17b/0x1b0
> [ 11.303332] mount_fs+0x35/0x150
> [ 11.303803] vfs_kern_mount.part.25+0x54/0x150
> [ 11.304443] do_mount+0x620/0xd60
> [ 11.304935] ? memdup_user+0x3e/0x70
> [ 11.305458] SyS_mount+0x80/0xd0
> [ 11.305931] mount_block_root+0x105/0x2b7
> [ 11.306512] ? SyS_mknod+0x16b/0x1f0
> [ 11.307035] ? set_debug_rodata+0x11/0x11
> [ 11.307616] prepare_namespace+0x135/0x16b
> [ 11.308215] kernel_init_freeable+0x271/0x297
> [ 11.308838] ? rest_init+0xd0/0xd0
> [ 11.309322] kernel_init+0xa/0x110
> [ 11.309821] ret_from_fork+0x3a/0x50
> [ 11.310347] Code: a5 45 31 ed e8 5d 5e 36 00 eb d7 48 c7 c7 20 48 2f a5 e8 4f 5e 36 00 eb c9 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 <48> 8b 87 40 04 00 00 48 8b 40 18 48 85 c0 74 05 e9 c6 7e 60 00
> [ 11.313168] RIP: fs_dax_release+0x5/0x90 RSP: ffffb1480062fbd8
> [ 11.313991] CR2: 0000000000000440
> [ 11.314475] ---[ end trace 8acbb19b74409665 ]---
>
>
> On Fri, Mar 30, 2018 at 09:03:08PM -0700, Dan Williams wrote:
> > In order to resolve collisions between filesystem operations and DMA to
> > DAX mapped pages we need a callback when DMA completes. With a callback
> > we can hold off filesystem operations while DMA is in-flight and then
> > resume those operations when the last put_page() occurs on a DMA page.
> >
> > Recall that the 'struct page' entries for DAX memory are created with
> > devm_memremap_pages(). That routine arranges for the pages to be
> > allocated, but never onlined, so a DAX page is DMA-idle when its
> > reference count reaches one.
> >
> > Also recall that the HMM sub-system added infrastructure to trap the
> > page-idle (2-to-1 reference count) transition of the pages allocated by
> > devm_memremap_pages() and trigger a callback via the 'struct
> > dev_pagemap' associated with the page range. Whereas the HMM callbacks
> > are going to a device driver to manage bounce pages in device-memory in
> > the filesystem-dax case we will call back to filesystem specified
> > callback.
> >
> > Since the callback is not known at devm_memremap_pages() time we arrange
> > for the filesystem to install it at mount time. No functional changes
> > are expected as this only registers a nop handler for the ->page_free()
> > event for device-mapped pages.
> >
> > Cc: Michal Hocko <mhocko@suse.com>
> > Reviewed-by: "Jérôme Glisse" <jglisse@redhat.com>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Reviewed-by: Jan Kara <jack@suse.cz>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > ---
> > drivers/dax/super.c | 21 +++++++++++----------
> > drivers/nvdimm/pmem.c | 3 ++-
> > fs/ext2/super.c | 6 +++---
> > fs/ext4/super.c | 6 +++---
> > fs/xfs/xfs_super.c | 20 ++++++++++----------
> > include/linux/dax.h | 23 ++++++++++++++---------
> > 6 files changed, 43 insertions(+), 36 deletions(-)
> >
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index c4cf284dfe1c..7d260f118a39 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -63,16 +63,6 @@ int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
> > }
> > EXPORT_SYMBOL(bdev_dax_pgoff);
> >
> > -#if IS_ENABLED(CONFIG_FS_DAX)
> > -struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
> > -{
> > - if (!blk_queue_dax(bdev->bd_queue))
> > - return NULL;
> > - return fs_dax_get_by_host(bdev->bd_disk->disk_name);
> > -}
> > -EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
> > -#endif
> > -
> > /**
> > * __bdev_dax_supported() - Check if the device supports dax for filesystem
> > * @sb: The superblock of the device
> > @@ -579,6 +569,17 @@ struct dax_device *alloc_dax(void *private, const char *__host,
> > }
> > EXPORT_SYMBOL_GPL(alloc_dax);
> >
> > +struct dax_device *alloc_dax_devmap(void *private, const char *host,
> > + const struct dax_operations *ops, struct dev_pagemap *pgmap)
> > +{
> > + struct dax_device *dax_dev = alloc_dax(private, host, ops);
> > +
> > + if (dax_dev)
> > + dax_dev->pgmap = pgmap;
> > + return dax_dev;
> > +}
> > +EXPORT_SYMBOL_GPL(alloc_dax_devmap);
> > +
> > void put_dax(struct dax_device *dax_dev)
> > {
> > if (!dax_dev)
> > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> > index 06f8dcc52ca6..e6d7351f3379 100644
> > --- a/drivers/nvdimm/pmem.c
> > +++ b/drivers/nvdimm/pmem.c
> > @@ -408,7 +408,8 @@ static int pmem_attach_disk(struct device *dev,
> > nvdimm_badblocks_populate(nd_region, &pmem->bb, &bb_res);
> > disk->bb = &pmem->bb;
> >
> > - dax_dev = alloc_dax(pmem, disk->disk_name, &pmem_dax_ops);
> > + dax_dev = alloc_dax_devmap(pmem, disk->disk_name, &pmem_dax_ops,
> > + &pmem->pgmap);
> > if (!dax_dev) {
> > put_disk(disk);
> > return -ENOMEM;
> > diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> > index 7666c065b96f..6ae20e319bc4 100644
> > --- a/fs/ext2/super.c
> > +++ b/fs/ext2/super.c
> > @@ -172,7 +172,7 @@ static void ext2_put_super (struct super_block * sb)
> > brelse (sbi->s_sbh);
> > sb->s_fs_info = NULL;
> > kfree(sbi->s_blockgroup_lock);
> > - fs_put_dax(sbi->s_daxdev);
> > + fs_dax_release(sbi->s_daxdev, sb);
> > kfree(sbi);
> > }
> >
> > @@ -817,7 +817,7 @@ static unsigned long descriptor_loc(struct super_block *sb,
> >
> > static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> > {
> > - struct dax_device *dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
> > + struct dax_device *dax_dev = fs_dax_claim_bdev(sb->s_bdev, sb);
> > struct buffer_head * bh;
> > struct ext2_sb_info * sbi;
> > struct ext2_super_block * es;
> > @@ -1213,7 +1213,7 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> > kfree(sbi->s_blockgroup_lock);
> > kfree(sbi);
> > failed:
> > - fs_put_dax(dax_dev);
> > + fs_dax_release(dax_dev, sb);
> > return ret;
> > }
> >
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index 39bf464c35f1..315a323729e3 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -952,7 +952,7 @@ static void ext4_put_super(struct super_block *sb)
> > if (sbi->s_chksum_driver)
> > crypto_free_shash(sbi->s_chksum_driver);
> > kfree(sbi->s_blockgroup_lock);
> > - fs_put_dax(sbi->s_daxdev);
> > + fs_dax_release(sbi->s_daxdev, sb);
> > kfree(sbi);
> > }
> >
> > @@ -3398,7 +3398,7 @@ static void ext4_set_resv_clusters(struct super_block *sb)
> >
> > static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> > {
> > - struct dax_device *dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
> > + struct dax_device *dax_dev = fs_dax_claim_bdev(sb->s_bdev, sb);
> > char *orig_data = kstrdup(data, GFP_KERNEL);
> > struct buffer_head *bh;
> > struct ext4_super_block *es = NULL;
> > @@ -4408,7 +4408,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> > out_free_base:
> > kfree(sbi);
> > kfree(orig_data);
> > - fs_put_dax(dax_dev);
> > + fs_dax_release(dax_dev, sb);
> > return err ? err : ret;
> > }
> >
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index 93588ea3d3d2..ef7dd7148c0b 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> > @@ -724,7 +724,7 @@ xfs_close_devices(
> >
> > xfs_free_buftarg(mp, mp->m_logdev_targp);
> > xfs_blkdev_put(logdev);
> > - fs_put_dax(dax_logdev);
> > + fs_dax_release(dax_logdev, mp);
> > }
> > if (mp->m_rtdev_targp) {
> > struct block_device *rtdev = mp->m_rtdev_targp->bt_bdev;
> > @@ -732,10 +732,10 @@ xfs_close_devices(
> >
> > xfs_free_buftarg(mp, mp->m_rtdev_targp);
> > xfs_blkdev_put(rtdev);
> > - fs_put_dax(dax_rtdev);
> > + fs_dax_release(dax_rtdev, mp);
> > }
> > xfs_free_buftarg(mp, mp->m_ddev_targp);
> > - fs_put_dax(dax_ddev);
> > + fs_dax_release(dax_ddev, mp);
> > }
> >
> > /*
> > @@ -753,9 +753,9 @@ xfs_open_devices(
> > struct xfs_mount *mp)
> > {
> > struct block_device *ddev = mp->m_super->s_bdev;
> > - struct dax_device *dax_ddev = fs_dax_get_by_bdev(ddev);
> > - struct dax_device *dax_logdev = NULL, *dax_rtdev = NULL;
> > + struct dax_device *dax_ddev = fs_dax_claim_bdev(ddev, mp);
> > struct block_device *logdev = NULL, *rtdev = NULL;
> > + struct dax_device *dax_logdev = NULL, *dax_rtdev = NULL;
> > int error;
> >
> > /*
> > @@ -765,7 +765,7 @@ xfs_open_devices(
> > error = xfs_blkdev_get(mp, mp->m_logname, &logdev);
> > if (error)
> > goto out;
> > - dax_logdev = fs_dax_get_by_bdev(logdev);
> > + dax_logdev = fs_dax_claim_bdev(logdev, mp);
> > }
> >
> > if (mp->m_rtname) {
> > @@ -779,7 +779,7 @@ xfs_open_devices(
> > error = -EINVAL;
> > goto out_close_rtdev;
> > }
> > - dax_rtdev = fs_dax_get_by_bdev(rtdev);
> > + dax_rtdev = fs_dax_claim_bdev(rtdev, mp);
> > }
> >
> > /*
> > @@ -813,14 +813,14 @@ xfs_open_devices(
> > xfs_free_buftarg(mp, mp->m_ddev_targp);
> > out_close_rtdev:
> > xfs_blkdev_put(rtdev);
> > - fs_put_dax(dax_rtdev);
> > + fs_dax_release(dax_rtdev, mp);
> > out_close_logdev:
> > if (logdev && logdev != ddev) {
> > xfs_blkdev_put(logdev);
> > - fs_put_dax(dax_logdev);
> > + fs_dax_release(dax_logdev, mp);
> > }
> > out:
> > - fs_put_dax(dax_ddev);
> > + fs_dax_release(dax_ddev, mp);
> > return error;
> > }
> >
> > diff --git a/include/linux/dax.h b/include/linux/dax.h
> > index e9d59a6b06e1..a88ff009e2a1 100644
> > --- a/include/linux/dax.h
> > +++ b/include/linux/dax.h
> > @@ -32,6 +32,8 @@ extern struct attribute_group dax_attribute_group;
> > struct dax_device *dax_get_by_host(const char *host);
> > struct dax_device *alloc_dax(void *private, const char *host,
> > const struct dax_operations *ops);
> > +struct dax_device *alloc_dax_devmap(void *private, const char *host,
> > + const struct dax_operations *ops, struct dev_pagemap *pgmap);
> > void put_dax(struct dax_device *dax_dev);
> > void kill_dax(struct dax_device *dax_dev);
> > void dax_write_cache(struct dax_device *dax_dev, bool wc);
> > @@ -50,6 +52,12 @@ static inline struct dax_device *alloc_dax(void *private, const char *host,
> > */
> > return NULL;
> > }
> > +static inline struct dax_device *alloc_dax_devmap(void *private,
> > + const char *host, const struct dax_operations *ops,
> > + struct dev_pagemap *pgmap)
> > +{
> > + return NULL;
> > +}
> > static inline void put_dax(struct dax_device *dax_dev)
> > {
> > }
> > @@ -79,12 +87,8 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
> > return dax_get_by_host(host);
> > }
> >
> > -static inline void fs_put_dax(struct dax_device *dax_dev)
> > -{
> > - put_dax(dax_dev);
> > -}
> > -
> > -struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
> > +struct dax_device *fs_dax_claim_bdev(struct block_device *bdev, void *owner);
> > +void fs_dax_release(struct dax_device *dax_dev, void *owner);
> > int dax_writeback_mapping_range(struct address_space *mapping,
> > struct block_device *bdev, struct writeback_control *wbc);
> > struct dax_device *fs_dax_claim(struct dax_device *dax_dev, void *owner);
> > @@ -100,13 +104,14 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
> > return NULL;
> > }
> >
> > -static inline void fs_put_dax(struct dax_device *dax_dev)
> > +static inline struct dax_device *fs_dax_claim_bdev(struct block_device *bdev,
> > + void *owner)
> > {
> > + return NULL;
> > }
> >
> > -static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
> > +static inline void fs_dax_release(struct dax_device *dax_dev, void *owner)
> > {
> > - return NULL;
> > }
> >
> > static inline int dax_writeback_mapping_range(struct address_space *mapping,

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