Re: [PATCH] btrfs: rework the order of btrfs_ordered_extent::flags

[Qu Wenruo]

On 2021/1/25 下午8:15, Filipe Manana wrote:

On Thu, Jan 21, 2021 at 4:52 PM David Sterba <dste...@suse.cz> wrote:

On Thu, Jan 21, 2021 at 02:13:54PM +0800, Qu Wenruo wrote:

[BUG]
There is a long existing bug in the last parameter of
btrfs_add_ordered_extent(), in commit 771ed689d2cd ("Btrfs: Optimize
compressed writeback and reads") back to 2008.

In that ancient commit btrfs_add_ordered_extent() expects the @type
parameter to be one of the following:
- BTRFS_ORDERED_REGULAR
- BTRFS_ORDERED_NOCOW
- BTRFS_ORDERED_PREALLOC
- BTRFS_ORDERED_COMPRESSED

But we pass 0 in cow_file_range(), which means BTRFS_ORDERED_IO_DONE.

Ironically extra check in __btrfs_add_ordered_extent() won't set the bit
if we're seeing (type == IO_DONE || type == IO_COMPLETE), and avoid any
obvious bug.

But this still leads to regular COW ordered extent having no bit to
indicate its type in various trace events, rendering REGULAR bit
useless.

[FIX]
This patch will change the following aspects to avoid such problem:
- Reorder btrfs_ordered_extent::flags
   Now the type bits go first (REGULAR/NOCOW/PREALLCO/COMPRESSED), then
   DIRECT bit, finally extra status bits like IO_DONE/COMPLETE/IOERR.

- Add extra ASSERT() for btrfs_add_ordered_extent_*()

- Remove @type parameter for btrfs_add_ordered_extent_compress()
   As the only valid @type here is BTRFS_ORDERED_COMPRESSED.

- Remove the unnecessary special check for IO_DONE/COMPLETE in
   __btrfs_add_ordered_extent()
   This is just to make the code work, with extra ASSERT(), there are
   limited values can be passed in.

Signed-off-by: Qu Wenruo <w...@suse.com>

Added to misc-next thanks.

Btw, I see that you added a Reviewed-by tag from me to the patch.
However I did not give the tag, not because I forgot but because there
was a small detail in a comment that should be fixed, which was not
addressed in misc-next.

And that comment update should not mention directIO completely.

Should I resend the patch with proper comment updated?

Thanks,
Qu

Thanks.

---
  fs/btrfs/inode.c             |  4 ++--
  fs/btrfs/ordered-data.c      | 18 +++++++++++++-----
  fs/btrfs/ordered-data.h      | 37 +++++++++++++++++++++++-------------
  include/trace/events/btrfs.h |  7 ++++---
  4 files changed, 43 insertions(+), 23 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ef6cb7b620d0..ea9056cc5559 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -917,7 +917,6 @@ static noinline void submit_compressed_extents(struct 
async_chunk *async_chunk)
                                               ins.objectid,
                                               async_extent->ram_size,
                                               ins.offset,
-                                             BTRFS_ORDERED_COMPRESSED,
                                               async_extent->compress_type);
               if (ret) {
                       btrfs_drop_extent_cache(inode, async_extent->start,
@@ -1127,7 +1126,8 @@ static noinline int cow_file_range(struct btrfs_inode 
*inode,
               free_extent_map(em);

               ret = btrfs_add_ordered_extent(inode, start, ins.objectid,
-                                            ram_size, cur_alloc_size, 0);
+                                            ram_size, cur_alloc_size,
+                                            BTRFS_ORDERED_REGULAR);
               if (ret)
                       goto out_drop_extent_cache;

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index d5d326c674b1..bd7e187d9b16 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -199,8 +199,11 @@ static int __btrfs_add_ordered_extent(struct btrfs_inode 
*inode, u64 file_offset
       entry->compress_type = compress_type;
       entry->truncated_len = (u64)-1;
       entry->qgroup_rsv = ret;
-     if (type != BTRFS_ORDERED_IO_DONE && type != BTRFS_ORDERED_COMPLETE)
-             set_bit(type, &entry->flags);
+
+     ASSERT(type == BTRFS_ORDERED_REGULAR || type == BTRFS_ORDERED_NOCOW ||
+            type == BTRFS_ORDERED_PREALLOC ||
+            type == BTRFS_ORDERED_COMPRESSED);

I've reformatted that so that all the checks are on separate lines, it's
easier to read though it does not fill the whole line.

+     set_bit(type, &entry->flags);

       if (dio) {
               percpu_counter_add_batch(&fs_info->dio_bytes, num_bytes,
@@ -256,6 +259,8 @@ int btrfs_add_ordered_extent(struct btrfs_inode *inode, u64 
file_offset,
                            u64 disk_bytenr, u64 num_bytes, u64 disk_num_bytes,
                            int type)
  {
+     ASSERT(type == BTRFS_ORDERED_REGULAR || type == BTRFS_ORDERED_NOCOW ||
+            type == BTRFS_ORDERED_PREALLOC);
       return __btrfs_add_ordered_extent(inode, file_offset, disk_bytenr,
                                         num_bytes, disk_num_bytes, type, 0,
                                         BTRFS_COMPRESS_NONE);
@@ -265,6 +270,8 @@ int btrfs_add_ordered_extent_dio(struct btrfs_inode *inode, 
u64 file_offset,
                                u64 disk_bytenr, u64 num_bytes,
                                u64 disk_num_bytes, int type)
  {
+     ASSERT(type == BTRFS_ORDERED_REGULAR || type == BTRFS_ORDERED_NOCOW ||
+            type == BTRFS_ORDERED_PREALLOC);
       return __btrfs_add_ordered_extent(inode, file_offset, disk_bytenr,
                                         num_bytes, disk_num_bytes, type, 1,
                                         BTRFS_COMPRESS_NONE);
@@ -272,11 +279,12 @@ int btrfs_add_ordered_extent_dio(struct btrfs_inode 
*inode, u64 file_offset,

  int btrfs_add_ordered_extent_compress(struct btrfs_inode *inode, u64 
file_offset,
                                     u64 disk_bytenr, u64 num_bytes,
-                                   u64 disk_num_bytes, int type,
-                                   int compress_type)
+                                   u64 disk_num_bytes, int compress_type)
  {
+     ASSERT(compress_type != BTRFS_COMPRESS_NONE);
       return __btrfs_add_ordered_extent(inode, file_offset, disk_bytenr,
-                                       num_bytes, disk_num_bytes, type, 0,
+                                       num_bytes, disk_num_bytes,
+                                       BTRFS_ORDERED_COMPRESSED, 0,
                                         compress_type);
  }

diff --git a/fs/btrfs/ordered-data.h b/fs/btrfs/ordered-data.h
index 46194c2c05d4..151ec6bba405 100644
--- a/fs/btrfs/ordered-data.h
+++ b/fs/btrfs/ordered-data.h
@@ -27,7 +27,7 @@ struct btrfs_ordered_sum {
  };

  /*
- * bits for the flags field:
+ * Bits for btrfs_ordered_extent::flags.
   *
   * BTRFS_ORDERED_IO_DONE is set when all of the blocks are written.
   * It is used to make sure metadata is inserted into the tree only once
@@ -38,24 +38,36 @@ struct btrfs_ordered_sum {
   * IO is done and any metadata is inserted into the tree.
   */
  enum {
+     /*
+      * Different types for direct io, one and only one of the 4 type can

direct io

+      * be set when creating ordered extent.
+      *
+      * REGULAR:     For regular non-compressed COW write
+      * NOCOW:       For NOCOW write into existing non-hole extent
+      * PREALLOC:    For NOCOW write into preallocated extent
+      * COMPRESSED:  For compressed COW write
+      */
+     BTRFS_ORDERED_REGULAR,
+     BTRFS_ORDERED_NOCOW,
+     BTRFS_ORDERED_PREALLOC,
+     BTRFS_ORDERED_COMPRESSED,
+
+     /*
+      * Extra bit for DirectIO, can only be set for

DirectIO

+      * REGULAR/NOCOW/PREALLOC. No DIO for compressed extent.

DIO

Three different ways to spell that but one is enough. Fixed.