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Subject[RFC PATCH v2 2/3] dm: expand hc_map in mapped_device for lack of map
Date
From: Huaisheng Ye <yehs1@lenovo.com>

Sometimes dm_swap_table couldn't be used in time.

For example, during the origin construction of
dm-snapshot, the sys_ioctl table_load will try to
detect the lower device origin-real whether support
direct access or not. But origin-real md's struct
dm-table pointer has not yet been assigned real address
in time by dev_suspend.

So I expand hc_map for get the address from struct
hash_cell directly in this case.

Here is the call trace, dm_dax_direct_access will call
dm_dax_get_live_target for get the struct dm_table pointer.

[ 213.975827] Call Trace:
[ 213.975832] dump_stack+0x5a/0x73
[ 213.975840] dm_dax_direct_access+0x12b/0x1b0 [dm_mod]
[ 213.975845] dax_direct_access+0x2d/0x60
[ 213.975848] __bdev_dax_supported+0x162/0x2a0
[ 213.975851] ? dump_stack+0x5a/0x73
[ 213.975859] device_supports_dax+0x15/0x20 [dm_mod]
[ 213.975867] dm_table_supports_dax.isra.13+0x7d/0xa0 [dm_mod]
[ 213.975875] dm_table_complete+0x3fb/0x750 [dm_mod]
[ 213.975883] table_load+0x19a/0x390 [dm_mod]
[ 213.975891] ? retrieve_status+0x1c0/0x1c0 [dm_mod]
[ 213.975898] ctl_ioctl+0x1d8/0x450 [dm_mod]
[ 213.975909] dm_ctl_ioctl+0xa/0x10 [dm_mod]
[ 213.975913] do_vfs_ioctl+0xa9/0x620
[ 213.975918] ? syscall_trace_enter+0x1c9/0x2b0
[ 213.975923] ksys_ioctl+0x60/0x90
[ 213.975927] __x64_sys_ioctl+0x16/0x20
[ 213.975931] do_syscall_64+0x5b/0x180
[ 213.975936] entry_SYSCALL_64_after_hwframe+0x44/0xa9

Signed-off-by: Huaisheng Ye <yehs1@lenovo.com>
---
drivers/md/dm-core.h | 1 +
drivers/md/dm-ioctl.c | 1 +
drivers/md/dm.c | 15 +++++++++++++++
3 files changed, 17 insertions(+)

diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index 224d445..5577d90 100644
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -40,6 +40,7 @@ struct mapped_device {
* dereference.
*/
void __rcu *map;
+ struct dm_table *hc_map;

unsigned long flags;

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index f666778..a27016e 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1365,6 +1365,7 @@ static int table_load(struct file *filp, struct dm_ioctl *param, size_t param_si
if (hc->new_map)
old_map = hc->new_map;
hc->new_map = t;
+ hc->md->hc_map = hc->new_map;
up_write(&_hash_lock);

param->flags |= DM_INACTIVE_PRESENT_FLAG;
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index c510179..19b48bb 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1080,6 +1080,21 @@ static struct dm_target *dm_dax_get_live_target(struct mapped_device *md,
struct dm_target *ti;

map = dm_get_live_table(md, srcu_idx);
+ if (!map) {
+ /* Sometimes dm_swap_table couldn't be used in time.
+ *
+ * For example, during the origin construction of
+ * dm-snapshot, the sys_ioctl table_load will try to
+ * detect the lower device origin-real whether support
+ * direct access or not. But origin-real device md's struct
+ * dm-table pointer has not yet been assigned real address.
+ * So hc_map has been used for get the address from
+ * struct hash_cell directly.
+ */
+ DMINFO("failed to get map, use hc_map insteadly");
+ map = md->hc_map;
+ }
+
if (!map)
return NULL;

--
1.8.3.1

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