Re: [PATCH v7 2/2] btrfs: Handle delalloc error correctly to avoid ordered extent hang

[Liu Bo]

On Wed, Mar 08, 2017 at 10:25:52AM +0800, Qu Wenruo wrote:
> [BUG]
> If run_delalloc_range() returns error and there is already some ordered
> extents created, btrfs will be hanged with the following backtrace:
> 
> Call Trace:
>  __schedule+0x2d4/0xae0
>  schedule+0x3d/0x90
>  btrfs_start_ordered_extent+0x160/0x200 [btrfs]
>  ? wake_atomic_t_function+0x60/0x60
>  btrfs_run_ordered_extent_work+0x25/0x40 [btrfs]
>  btrfs_scrubparity_helper+0x1c1/0x620 [btrfs]
>  btrfs_flush_delalloc_helper+0xe/0x10 [btrfs]
>  process_one_work+0x2af/0x720
>  ? process_one_work+0x22b/0x720
>  worker_thread+0x4b/0x4f0
>  kthread+0x10f/0x150
>  ? process_one_work+0x720/0x720
>  ? kthread_create_on_node+0x40/0x40
>  ret_from_fork+0x2e/0x40
> 
> [CAUSE]
> 
> |<-- delalloc range --->|
> | OE 1 | OE 2 | ... | OE n |
> |<>|   |<-- cleanup range ->|
>  ||
>  \_=> First page handled by end_extent_writepage() in __extent_writepage()
> 
> The problem is caused by error handler of run_delalloc_range(), which
> doesn't handle any created ordered extents, leaving them waiting on
> btrfs_finish_ordered_io() to finish.
> 
> However after run_delalloc_range() returns error, __extent_writepage()
> won't submit bio, so btrfs_writepage_end_io_hook() won't be triggered
> except the first page, and btrfs_finish_ordered_io() won't be triggered
> for created ordered extents either.
> 
> So OE 2~n will hang forever, and if OE 1 is larger than one page, it
> will also hang.
> 
> [FIX]
> Introduce btrfs_cleanup_ordered_extents() function to cleanup created
> ordered extents and finish them manually.
> 
> The function is based on existing
> btrfs_endio_direct_write_update_ordered() function, and modify it to
> act just like btrfs_writepage_endio_hook() but handles specified range
> other than one page.
> 
> After fix, delalloc error will be handled like:
> 
> |<-- delalloc range --->|
> | OE 1 | OE 2 | ... | OE n |
> |<>|<  --->|<-- old error handler ->|
>  ||  ||
>  ||  \_=> Cleaned up by cleanup_ordered_extents()
>  \_=> First page handled by end_extent_writepage() in __extent_writepage()

Reviewed-by: Liu Bo 

Thanks,

-liubo
> 
> Signed-off-by: Qu Wenruo 
> Signed-off-by: Filipe Manana 
> ---
> v2:
>   Add BTRFS_ORDERED_SKIP_METADATA flag to avoid double reducing
>   outstanding extents, which is already done by
>   extent_clear_unlock_delalloc() with EXTENT_DO_ACCOUNT control bit
> v3:
>   Skip first page to avoid underflow ordered->bytes_left.
>   Fix range passed in cow_file_range() which doesn't cover the whole
>   extent.
>   Expend extent_clear_unlock_delalloc() range to allow them to handle
>   metadata release.
> v4:
>   Don't use extra bit to skip metadata freeing for ordered extent,
>   but only handle btrfs_reloc_clone_csums() error just before processing
>   next extent.
>   This makes error handle much easier for run_delalloc_nocow().
> v5:
>   Variant gramma and comment fixes suggested by Filipe Manana
>   Enhanced commit message to focus on the generic error handler bug,
>   pointed out by Filipe Manana
>   Adding missing wq/func user in __endio_write_update_ordered(), pointed
>   out by Filipe Manana.
>   Enhanced commit message with ascii art to explain the bug more easily.
>   Fix a bug which can leads to corrupted extent allocation, exposed by
>   Filipe Manana.
> v6:
>   Split the metadata underflow fix to another patch.
>   Use better comment and btrfs_cleanup_ordered_extent() implementation
>   from Filipe Manana.
> v7:
>   Add back const prefix
> ---
>  fs/btrfs/inode.c | 63 
> ++--
>  1 file changed, 48 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index fe588bf30d02..d3bc68bbe0e7 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -115,6 +115,31 @@ static struct extent_map *create_io_em(struct inode 
> *inode, u64 start, u64 len,
>  u64 ram_bytes, int compress_type,
>  int type);
>  
> +static void __endio_write_update_ordered(struct inode *inode,
> +  const u64 offset, const u64 bytes,
> +  const bool uptodate);
> +
> +/*
> + * Cleanup all submitted ordered extents in specified range to handle errors
> + * from the fill_dellaloc() callback.
> + *
> + * NOTE: caller must ensure that when an error happens, it can not call
> + * extent_clear_unlock_delalloc() to clear both the bits EXTENT_DO_ACCOUNTING
> + * and EXTENT_DELALLOC simultaneously, because that causes the reserved 
> metadata
> + * to be released, which we want to happen only when finishing the ordered
> + * extent (btrfs_finish_ordered_io()). Also note that the caller of the
> + * fill_delalloc() 

Re: [PATCH v7 2/2] btrfs: Handle delalloc error correctly to avoid ordered extent hang

[Filipe Manana]

On Wed, Mar 8, 2017 at 2:25 AM, Qu Wenruo  wrote:
> [BUG]
> If run_delalloc_range() returns error and there is already some ordered
> extents created, btrfs will be hanged with the following backtrace:
>
> Call Trace:
>  __schedule+0x2d4/0xae0
>  schedule+0x3d/0x90
>  btrfs_start_ordered_extent+0x160/0x200 [btrfs]
>  ? wake_atomic_t_function+0x60/0x60
>  btrfs_run_ordered_extent_work+0x25/0x40 [btrfs]
>  btrfs_scrubparity_helper+0x1c1/0x620 [btrfs]
>  btrfs_flush_delalloc_helper+0xe/0x10 [btrfs]
>  process_one_work+0x2af/0x720
>  ? process_one_work+0x22b/0x720
>  worker_thread+0x4b/0x4f0
>  kthread+0x10f/0x150
>  ? process_one_work+0x720/0x720
>  ? kthread_create_on_node+0x40/0x40
>  ret_from_fork+0x2e/0x40
>
> [CAUSE]
>
> |<-- delalloc range --->|
> | OE 1 | OE 2 | ... | OE n |
> |<>|   |<-- cleanup range ->|
>  ||
>  \_=> First page handled by end_extent_writepage() in __extent_writepage()
>
> The problem is caused by error handler of run_delalloc_range(), which
> doesn't handle any created ordered extents, leaving them waiting on
> btrfs_finish_ordered_io() to finish.
>
> However after run_delalloc_range() returns error, __extent_writepage()
> won't submit bio, so btrfs_writepage_end_io_hook() won't be triggered
> except the first page, and btrfs_finish_ordered_io() won't be triggered
> for created ordered extents either.
>
> So OE 2~n will hang forever, and if OE 1 is larger than one page, it
> will also hang.
>
> [FIX]
> Introduce btrfs_cleanup_ordered_extents() function to cleanup created
> ordered extents and finish them manually.
>
> The function is based on existing
> btrfs_endio_direct_write_update_ordered() function, and modify it to
> act just like btrfs_writepage_endio_hook() but handles specified range
> other than one page.
>
> After fix, delalloc error will be handled like:
>
> |<-- delalloc range --->|
> | OE 1 | OE 2 | ... | OE n |
> |<>|<  --->|<-- old error handler ->|
>  ||  ||
>  ||  \_=> Cleaned up by cleanup_ordered_extents()
>  \_=> First page handled by end_extent_writepage() in __extent_writepage()
>
> Signed-off-by: Qu Wenruo 

Reviewed-by: Filipe Manana 

thanks

> Signed-off-by: Filipe Manana 
> ---
> v2:
>   Add BTRFS_ORDERED_SKIP_METADATA flag to avoid double reducing
>   outstanding extents, which is already done by
>   extent_clear_unlock_delalloc() with EXTENT_DO_ACCOUNT control bit
> v3:
>   Skip first page to avoid underflow ordered->bytes_left.
>   Fix range passed in cow_file_range() which doesn't cover the whole
>   extent.
>   Expend extent_clear_unlock_delalloc() range to allow them to handle
>   metadata release.
> v4:
>   Don't use extra bit to skip metadata freeing for ordered extent,
>   but only handle btrfs_reloc_clone_csums() error just before processing
>   next extent.
>   This makes error handle much easier for run_delalloc_nocow().
> v5:
>   Variant gramma and comment fixes suggested by Filipe Manana
>   Enhanced commit message to focus on the generic error handler bug,
>   pointed out by Filipe Manana
>   Adding missing wq/func user in __endio_write_update_ordered(), pointed
>   out by Filipe Manana.
>   Enhanced commit message with ascii art to explain the bug more easily.
>   Fix a bug which can leads to corrupted extent allocation, exposed by
>   Filipe Manana.
> v6:
>   Split the metadata underflow fix to another patch.
>   Use better comment and btrfs_cleanup_ordered_extent() implementation
>   from Filipe Manana.
> v7:
>   Add back const prefix
> ---
>  fs/btrfs/inode.c | 63 
> ++--
>  1 file changed, 48 insertions(+), 15 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index fe588bf30d02..d3bc68bbe0e7 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -115,6 +115,31 @@ static struct extent_map *create_io_em(struct inode 
> *inode, u64 start, u64 len,
>u64 ram_bytes, int compress_type,
>int type);
>
> +static void __endio_write_update_ordered(struct inode *inode,
> +const u64 offset, const u64 bytes,
> +const bool uptodate);
> +
> +/*
> + * Cleanup all submitted ordered extents in specified range to handle errors
> + * from the fill_dellaloc() callback.
> + *
> + * NOTE: caller must ensure that when an error happens, it can not call
> + * extent_clear_unlock_delalloc() to clear both the bits EXTENT_DO_ACCOUNTING
> + * and EXTENT_DELALLOC simultaneously, because that causes the reserved 
> metadata
> + * to be released, which we want to happen only when finishing the ordered
> + * extent (btrfs_finish_ordered_io()). Also note that the caller of the
> + * 

[PATCH v7 2/2] btrfs: Handle delalloc error correctly to avoid ordered extent hang

[Qu Wenruo]

[BUG]
If run_delalloc_range() returns error and there is already some ordered
extents created, btrfs will be hanged with the following backtrace:

Call Trace:
 __schedule+0x2d4/0xae0
 schedule+0x3d/0x90
 btrfs_start_ordered_extent+0x160/0x200 [btrfs]
 ? wake_atomic_t_function+0x60/0x60
 btrfs_run_ordered_extent_work+0x25/0x40 [btrfs]
 btrfs_scrubparity_helper+0x1c1/0x620 [btrfs]
 btrfs_flush_delalloc_helper+0xe/0x10 [btrfs]
 process_one_work+0x2af/0x720
 ? process_one_work+0x22b/0x720
 worker_thread+0x4b/0x4f0
 kthread+0x10f/0x150
 ? process_one_work+0x720/0x720
 ? kthread_create_on_node+0x40/0x40
 ret_from_fork+0x2e/0x40

[CAUSE]

|<-- delalloc range --->|
| OE 1 | OE 2 | ... | OE n |
|<>|   |<-- cleanup range ->|
 ||
 \_=> First page handled by end_extent_writepage() in __extent_writepage()

The problem is caused by error handler of run_delalloc_range(), which
doesn't handle any created ordered extents, leaving them waiting on
btrfs_finish_ordered_io() to finish.

However after run_delalloc_range() returns error, __extent_writepage()
won't submit bio, so btrfs_writepage_end_io_hook() won't be triggered
except the first page, and btrfs_finish_ordered_io() won't be triggered
for created ordered extents either.

So OE 2~n will hang forever, and if OE 1 is larger than one page, it
will also hang.

[FIX]
Introduce btrfs_cleanup_ordered_extents() function to cleanup created
ordered extents and finish them manually.

The function is based on existing
btrfs_endio_direct_write_update_ordered() function, and modify it to
act just like btrfs_writepage_endio_hook() but handles specified range
other than one page.

After fix, delalloc error will be handled like:

|<-- delalloc range --->|
| OE 1 | OE 2 | ... | OE n |
|<>|<  --->|<-- old error handler ->|
 ||  ||
 ||  \_=> Cleaned up by cleanup_ordered_extents()
 \_=> First page handled by end_extent_writepage() in __extent_writepage()

Signed-off-by: Qu Wenruo 
Signed-off-by: Filipe Manana 
---
v2:
  Add BTRFS_ORDERED_SKIP_METADATA flag to avoid double reducing
  outstanding extents, which is already done by
  extent_clear_unlock_delalloc() with EXTENT_DO_ACCOUNT control bit
v3:
  Skip first page to avoid underflow ordered->bytes_left.
  Fix range passed in cow_file_range() which doesn't cover the whole
  extent.
  Expend extent_clear_unlock_delalloc() range to allow them to handle
  metadata release.
v4:
  Don't use extra bit to skip metadata freeing for ordered extent,
  but only handle btrfs_reloc_clone_csums() error just before processing
  next extent.
  This makes error handle much easier for run_delalloc_nocow().
v5:
  Variant gramma and comment fixes suggested by Filipe Manana
  Enhanced commit message to focus on the generic error handler bug,
  pointed out by Filipe Manana
  Adding missing wq/func user in __endio_write_update_ordered(), pointed
  out by Filipe Manana.
  Enhanced commit message with ascii art to explain the bug more easily.
  Fix a bug which can leads to corrupted extent allocation, exposed by
  Filipe Manana.
v6:
  Split the metadata underflow fix to another patch.
  Use better comment and btrfs_cleanup_ordered_extent() implementation
  from Filipe Manana.
v7:
  Add back const prefix
---
 fs/btrfs/inode.c | 63 ++--
 1 file changed, 48 insertions(+), 15 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index fe588bf30d02..d3bc68bbe0e7 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -115,6 +115,31 @@ static struct extent_map *create_io_em(struct inode 
*inode, u64 start, u64 len,
   u64 ram_bytes, int compress_type,
   int type);
 
+static void __endio_write_update_ordered(struct inode *inode,
+const u64 offset, const u64 bytes,
+const bool uptodate);
+
+/*
+ * Cleanup all submitted ordered extents in specified range to handle errors
+ * from the fill_dellaloc() callback.
+ *
+ * NOTE: caller must ensure that when an error happens, it can not call
+ * extent_clear_unlock_delalloc() to clear both the bits EXTENT_DO_ACCOUNTING
+ * and EXTENT_DELALLOC simultaneously, because that causes the reserved 
metadata
+ * to be released, which we want to happen only when finishing the ordered
+ * extent (btrfs_finish_ordered_io()). Also note that the caller of the
+ * fill_delalloc() callback already does proper cleanup for the first page of
+ * the range, that is, it invokes the callback writepage_end_io_hook() for the
+ * range of the first page.
+ */
+static inline void btrfs_cleanup_ordered_extents(struct inode *inode,
+const u64 offset,
+