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author | Dave Airlie <airlied@redhat.com> | 2020-07-24 01:28:09 +0300 |
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committer | Dave Airlie <airlied@redhat.com> | 2020-07-24 01:48:05 +0300 |
commit | 41206a073ceebc517245677a19f52ba6379b33a9 (patch) | |
tree | 2fc35aac6abe32b99058ad55b0fc6e4d449d1056 /fs/btrfs/extent_io.c | |
parent | 206739119508d5ab4b42ab480ff61a7e6cd72d7c (diff) | |
parent | ba47d845d715a010f7b51f6f89bae32845e6acb7 (diff) | |
download | linux-41206a073ceebc517245677a19f52ba6379b33a9.tar.xz |
Merge v5.8-rc6 into drm-next
I've got a silent conflict + two trees based on fixes to merge.
Fixes a silent merge with amdgpu
Signed-off-by: Dave Airlie <airlied@redhat.com>
Diffstat (limited to 'fs/btrfs/extent_io.c')
-rw-r--r-- | fs/btrfs/extent_io.c | 40 |
1 files changed, 24 insertions, 16 deletions
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 68c96057ad2d..608f93438b29 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -5058,25 +5058,28 @@ struct extent_buffer *alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info, static void check_buffer_tree_ref(struct extent_buffer *eb) { int refs; - /* the ref bit is tricky. We have to make sure it is set - * if we have the buffer dirty. Otherwise the - * code to free a buffer can end up dropping a dirty - * page + /* + * The TREE_REF bit is first set when the extent_buffer is added + * to the radix tree. It is also reset, if unset, when a new reference + * is created by find_extent_buffer. * - * Once the ref bit is set, it won't go away while the - * buffer is dirty or in writeback, and it also won't - * go away while we have the reference count on the - * eb bumped. + * It is only cleared in two cases: freeing the last non-tree + * reference to the extent_buffer when its STALE bit is set or + * calling releasepage when the tree reference is the only reference. * - * We can't just set the ref bit without bumping the - * ref on the eb because free_extent_buffer might - * see the ref bit and try to clear it. If this happens - * free_extent_buffer might end up dropping our original - * ref by mistake and freeing the page before we are able - * to add one more ref. + * In both cases, care is taken to ensure that the extent_buffer's + * pages are not under io. However, releasepage can be concurrently + * called with creating new references, which is prone to race + * conditions between the calls to check_buffer_tree_ref in those + * codepaths and clearing TREE_REF in try_release_extent_buffer. * - * So bump the ref count first, then set the bit. If someone - * beat us to it, drop the ref we added. + * The actual lifetime of the extent_buffer in the radix tree is + * adequately protected by the refcount, but the TREE_REF bit and + * its corresponding reference are not. To protect against this + * class of races, we call check_buffer_tree_ref from the codepaths + * which trigger io after they set eb->io_pages. Note that once io is + * initiated, TREE_REF can no longer be cleared, so that is the + * moment at which any such race is best fixed. */ refs = atomic_read(&eb->refs); if (refs >= 2 && test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) @@ -5527,6 +5530,11 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num) clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags); eb->read_mirror = 0; atomic_set(&eb->io_pages, num_reads); + /* + * It is possible for releasepage to clear the TREE_REF bit before we + * set io_pages. See check_buffer_tree_ref for a more detailed comment. + */ + check_buffer_tree_ref(eb); for (i = 0; i < num_pages; i++) { page = eb->pages[i]; |