For files with logical blocks close to EXT_MAX_BLOCKS, the file size predicted in ext4_mb_normalize_request() may exceed EXT_MAX_BLOCKS. This can cause some blocks to be preallocated that will not be used. And after [Fixes], the following issue may be triggered: ========================================================= kernel BUG at fs/ext4/mballoc.c:4653! Internal error: Oops - BUG: 00000000f2000800 [#1] SMP CPU: 1 PID: 2357 Comm: xfs_io 6.7.0-rc2-00195-g0f5cc96c367f Hardware name: linux,dummy-virt (DT) pc : ext4_mb_use_inode_pa+0x148/0x208 lr : ext4_mb_use_inode_pa+0x98/0x208 Call trace: ext4_mb_use_inode_pa+0x148/0x208 ext4_mb_new_inode_pa+0x240/0x4a8 ext4_mb_use_best_found+0x1d4/0x208 ext4_mb_try_best_found+0xc8/0x110 ext4_mb_regular_allocator+0x11c/0xf48 ext4_mb_new_blocks+0x790/0xaa8 ext4_ext_map_blocks+0x7cc/0xd20 ext4_map_blocks+0x170/0x600 ext4_iomap_begin+0x1c0/0x348 ========================================================= Here is a calculation when adjusting ac_b_ex in ext4_mb_new_inode_pa(): ex.fe_logical = orig_goal_end - EXT4_C2B(sbi, ex.fe_len); if (ac->ac_o_ex.fe_logical >= ex.fe_logical) goto adjust_bex; The problem is that when orig_goal_end is subtracted from ac_b_ex.fe_len it is still greater than EXT_MAX_BLOCKS, which causes ex.fe_logical to overflow to a very small value, which ultimately triggers a BUG_ON in ext4_mb_new_inode_pa() because pa->pa_free < len. The last logical block of an actual write request does not exceed EXT_MAX_BLOCKS, so in ext4_mb_normalize_request() also avoids normalizing the last logical block to exceed EXT_MAX_BLOCKS to avoid the above issue. The test case in [Link] can reproduce the above issue with 64k block size. Link: https://patchwork.kernel.org/project/fstests/list/?series=804003 Cc: stable@xxxxxxxxxx # 6.4 Fixes: 93cdf49f6eca ("ext4: Fix best extent lstart adjustment logic in ext4_mb_new_inode_pa()") Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx> --- fs/ext4/mballoc.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 454d5612641e..d72b5e3c92ec 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -4478,6 +4478,10 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac, start = max(start, rounddown(ac->ac_o_ex.fe_logical, (ext4_lblk_t)EXT4_BLOCKS_PER_GROUP(ac->ac_sb))); + /* avoid unnecessary preallocation that may trigger assertions */ + if (start + size > EXT_MAX_BLOCKS) + size = EXT_MAX_BLOCKS - start; + /* don't cover already allocated blocks in selected range */ if (ar->pleft && start <= ar->lleft) { size -= ar->lleft + 1 - start; -- 2.31.1
