[PATCH 6.4 056/800] btrfs: dont fail writeback when allocating the compression context fails

Greg Kroah-Hartman
2023-07-16T19:56:43Z

From: Christoph Hellwig <hch@lst.de>

[ Upstream commit 973fb26e81a9f59dfe45b079a698c0e238f7bf69 ]

If cow_file_range_async fails to allocate the asynchronous writeback
context, it currently returns an error and entirely fails the writeback.
This is not a good idea as a writeback failure is a non-temporary error
condition that will make the file system unusable. Just fall back to
synchronous uncompressed writeback instead. This requires us to delay
setting the BTRFS_INODE_HAS_ASYNC_EXTENT flag until we've committed to
the async writeback.

The compression checks INODE_NOCOMPRESS and FORCE_COMPRESS are moved
from cow_file_range_async to the preceding checks btrfs_run_delalloc_range().

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Stable-dep-of: 7027f87108ce ("btrfs: don't treat zoned writeback as being from an async helper thread")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/inode.c | 74 ++++++++++++++++++------------------------------
1 file changed, 28 insertions(+), 46 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 7fcafcc5292c8..3d12dba145152 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1521,58 +1521,36 @@ static noinline void async_cow_free(struct btrfs_work *work)
kvfree(async_cow);
}

-static int cow_file_range_async(struct btrfs_inode *inode,
- struct writeback_control *wbc,
- struct page *locked_page,
- u64 start, u64 end, int *page_started,
- unsigned long *nr_written)
+static bool cow_file_range_async(struct btrfs_inode *inode,
+ struct writeback_control *wbc,
+ struct page *locked_page,
+ u64 start, u64 end, int *page_started,
+ unsigned long *nr_written)
{
struct btrfs_fs_info *fs_info = inode->root->fs_info;
struct cgroup_subsys_state *blkcg_css = wbc_blkcg_css(wbc);
struct async_cow *ctx;
struct async_chunk *async_chunk;
unsigned long nr_pages;
- u64 cur_end;
u64 num_chunks = DIV_ROUND_UP(end - start, SZ_512K);
int i;
- bool should_compress;
unsigned nofs_flag;
const blk_opf_t write_flags = wbc_to_write_flags(wbc);

- unlock_extent(&inode->io_tree, start, end, NULL);
-
- if (inode->flags & BTRFS_INODE_NOCOMPRESS &&
- !btrfs_test_opt(fs_info, FORCE_COMPRESS)) {
- num_chunks = 1;
- should_compress = false;
- } else {
- should_compress = true;
- }
-
nofs_flag = memalloc_nofs_save();
ctx = kvmalloc(struct_size(ctx, chunks, num_chunks), GFP_KERNEL);
memalloc_nofs_restore(nofs_flag);
+ if (!ctx)
+ return false;

- if (!ctx) {
- unsigned clear_bits = EXTENT_LOCKED | EXTENT_DELALLOC |
- EXTENT_DELALLOC_NEW | EXTENT_DEFRAG |
- EXTENT_DO_ACCOUNTING;
- unsigned long page_ops = PAGE_UNLOCK | PAGE_START_WRITEBACK |
- PAGE_END_WRITEBACK | PAGE_SET_ERROR;
-
- extent_clear_unlock_delalloc(inode, start, end, locked_page,
- clear_bits, page_ops);
- return -ENOMEM;
- }
+ unlock_extent(&inode->io_tree, start, end, NULL);
+ set_bit(BTRFS_INODE_HAS_ASYNC_EXTENT, &inode->runtime_flags);

async_chunk = ctx->chunks;
atomic_set(&ctx->num_chunks, num_chunks);

for (i = 0; i < num_chunks; i++) {
- if (should_compress)
- cur_end = min(end, start + SZ_512K - 1);
- else
- cur_end = end;
+ u64 cur_end = min(end, start + SZ_512K - 1);

/*
* igrab is called higher up in the call chain, take only the
@@ -1633,7 +1611,7 @@ static int cow_file_range_async(struct btrfs_inode *inode,
start = cur_end + 1;
}
*page_started = 1;
- return 0;
+ return true;
}

static noinline int run_delalloc_zoned(struct btrfs_inode *inode,
@@ -2214,7 +2192,7 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct page *locked_page
u64 start, u64 end, int *page_started, unsigned long *nr_written,
struct writeback_control *wbc)
{
- int ret;
+ int ret = 0;
const bool zoned = btrfs_is_zoned(inode->root->fs_info);

/*
@@ -2235,19 +2213,23 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct page *locked_page
ASSERT(!zoned || btrfs_is_data_reloc_root(inode->root));
ret = run_delalloc_nocow(inode, locked_page, start, end,
page_started, nr_written);
- } else if (!btrfs_inode_can_compress(inode) ||
- !inode_need_compress(inode, start, end)) {
- if (zoned)
- ret = run_delalloc_zoned(inode, locked_page, start, end,
- page_started, nr_written);
- else
- ret = cow_file_range(inode, locked_page, start, end,
- page_started, nr_written, 1, NULL);
- } else {
- set_bit(BTRFS_INODE_HAS_ASYNC_EXTENT, &inode->runtime_flags);
- ret = cow_file_range_async(inode, wbc, locked_page, start, end,
- page_started, nr_written);
+ goto out;
}
+
+ if (btrfs_inode_can_compress(inode) &&
+ inode_need_compress(inode, start, end) &&
+ cow_file_range_async(inode, wbc, locked_page, start,
+ end, page_started, nr_written))
+ goto out;
+
+ if (zoned)
+ ret = run_delalloc_zoned(inode, locked_page, start, end,
+ page_started, nr_written);
+ else
+ ret = cow_file_range(inode, locked_page, start, end,
+ page_started, nr_written, 1, NULL);
+
+out:
ASSERT(ret <= 0);
if (ret)
btrfs_cleanup_ordered_extents(inode, locked_page, start,
--
2.39.2