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ext4: prevent the normalized size from exceeding EXT_MAX_BLOCKS

Carlos Maiolino requested to merge cmaiolino/centos-stream-9:el94_rhel21161 into main

JIRA: https://issues.redhat.com/browse/RHEL-21161 Tested: Using xfstests

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@kernel.org # 6.4 Fixes: 93cdf49f6eca ("ext4: Fix best extent lstart adjustment logic in ext4_mb_new_inode_pa()") Signed-off-by: Baokun Li libaokun1@huawei.com Reviewed-by: Jan Kara jack@suse.cz Link: https://lore.kernel.org/r/20231127063313.3734294-1-libaokun1@huawei.com Signed-off-by: Theodore Ts'o tytso@mit.edu (cherry picked from commit 2dcf5fde6dffb312a4bfb8ef940cea2d1f402e32) Signed-off-by: Carlos Maiolino cmaiolino@redhat.com

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