From: Josef Bacik <josef@xxxxxxxxxxxxxx>
commit 17b17fcd6d446b95904a6929c40012ee7f0afc0c upstream.
While trying to get the subpage blocksize tests running, I hit the
following panic on generic/476
assertion failed: PagePrivate(page) && page->private, in fs/btrfs/subpage.c:229
kernel BUG at fs/btrfs/subpage.c:229!
Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
CPU: 1 PID: 1453 Comm: fsstress Not tainted 6.4.0-rc7+ #12
Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20230301gitf80f052277c8-26.fc38 03/01/2023
pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
pc : btrfs_subpage_assert+0xbc/0xf0
lr : btrfs_subpage_assert+0xbc/0xf0
Call trace:
btrfs_subpage_assert+0xbc/0xf0
btrfs_subpage_clear_checked+0x38/0xc0
btrfs_page_clear_checked+0x48/0x98
btrfs_truncate_block+0x5d0/0x6a8
btrfs_cont_expand+0x5c/0x528
btrfs_write_check.isra.0+0xf8/0x150
btrfs_buffered_write+0xb4/0x760
btrfs_do_write_iter+0x2f8/0x4b0
btrfs_file_write_iter+0x1c/0x30
do_iter_readv_writev+0xc8/0x158
do_iter_write+0x9c/0x210
vfs_iter_write+0x24/0x40
iter_file_splice_write+0x224/0x390
direct_splice_actor+0x38/0x68
splice_direct_to_actor+0x12c/0x260
do_splice_direct+0x90/0xe8
generic_copy_file_range+0x50/0x90
vfs_copy_file_range+0x29c/0x470
__arm64_sys_copy_file_range+0xcc/0x498
invoke_syscall.constprop.0+0x80/0xd8
do_el0_svc+0x6c/0x168
el0_svc+0x50/0x1b0
el0t_64_sync_handler+0x114/0x120
el0t_64_sync+0x194/0x198
This happens because during btrfs_cont_expand we'll get a page, set it
as mapped, and if it's not Uptodate we'll read it. However between the
read and re-locking the page we could have called release_folio() on the
page, but left the page in the file mapping. release_folio() can clear
the page private, and thus further down we blow up when we go to modify
the subpage bits.
Fix this by putting the set_page_extent_mapped() after the read. This
is safe because read_folio() will call set_page_extent_mapped() before
it does the read, and then if we clear page private but leave it on the
mapping we're completely safe re-setting set_page_extent_mapped(). With
this patch I can now run generic/476 without panicing.
CC: stable@xxxxxxxxxxxxxxx # 6.1+
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/inode.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4913,9 +4913,6 @@ again:
ret = -ENOMEM;
goto out;
}
- ret = set_page_extent_mapped(page);
- if (ret < 0)
- goto out_unlock;
if (!PageUptodate(page)) {
ret = btrfs_read_folio(NULL, page_folio(page));
@@ -4930,6 +4927,17 @@ again:
goto out_unlock;
}
}
+
+ /*
+ * We unlock the page after the io is completed and then re-lock it
+ * above. release_folio() could have come in between that and cleared
+ * PagePrivate(), but left the page in the mapping. Set the page mapped
+ * here to make sure it's properly set for the subpage stuff.
+ */
+ ret = set_page_extent_mapped(page);
+ if (ret < 0)
+ goto out_unlock;
+
wait_on_page_writeback(page);
lock_extent(io_tree, block_start, block_end, &cached_state);
