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btrfs: disable large folios for systems with highmem

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[BUG]
There is a bug report that on 32bit systems (i686), btrfs crashes when
trying to do zstd compression:

  BUG: unable to handle page fault for address: fffbc000
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  CPU: 0 UID: 0 PID: 61 Comm: kworker/u8:5 Tainted: G                 N  7.2.0-rc3-P3 #2 PREEMPTLAZY
  Hardware name: LENOVO 2007F2G/2007F2G, BIOS 79ETE7WW (2.27 ) 03/21/2011
  Workqueue: btrfs-delalloc btrfs_work_helper
  EIP: ZSTD_compressStream2+0x221/0x5fc
  Call Trace:
   ZSTD_compressStream+0xd/0x48
   zstd_compress_stream+0x8/0x10
   zstd_compress_bio+0x20a/0x564
   btrfs_compress_bio+0x94/0xc0
   compress_file_range+0x20a/0x380
   btrfs_work_helper+0xc1/0x1b4
   process_scheduled_works+0x15f/0x204
   worker_thread+0x10c/0x178
   kthread+0xe1/0xe8
   ret_from_fork+0x1d/0x14c
   ret_from_fork_asm+0x12/0x18
   entry_INT80_32+0xf0/0xf0
  CR2: 00000000fffbc000
  ---[ end trace 0000000000000000 ]---

[CAUSE]
Inside zstd_compress_bio(), we assume the whole page cache folio can be
mapped in one go.

However that assumption is not true on systems with CONFIG_HIGHMEM, the
pages of the large folio can be in HIGHMEM, which needs to be mapped
before access.

Meanwhile zstd_compress_bio() only map the page of a large folio where
the start filepos is, the remaining pages are not mapped, and accessing
the remaining pages will trigger the above crash.

[FIX]
Do not enable large folios when the kernel has CONFIG_HIGHMEM enabled.

This is the same handling for bs > ps support.

Link: https://github.com/kdave/btrfs-progs/issues/1146
Reported-by: Erhard Furtner <erhard_f@mailbox.org>
Fixes: 9bce95edb1 ("btrfs: move large data folios out of experimental features")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo
2026-07-20 19:19:41 +09:30
committed by David Sterba
parent c4c0673e4c
commit 7f03a417fc
1 changed files with 9 additions and 1 deletions
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10
fs/btrfs/disk-io.c
View File

@@ -3468,7 +3468,15 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
fs_info->sectorsize = sectorsize;
fs_info->sectorsize_bits = ilog2(sectorsize);
fs_info->block_min_order = ilog2(round_up(sectorsize, PAGE_SIZE) >> PAGE_SHIFT);
fs_info->block_max_order = calc_block_max_order(fs_info->sectorsize_bits);
/*
* For HIGHMEM, a large folio cannot be mapped in one go, breaking a lot
* of basic assumptions for btrfs IOs.
* Disable large folios for such 32-bit systems.
*/
if (IS_ENABLED(CONFIG_HIGHMEM))
fs_info->block_max_order = fs_info->block_min_order;
else
fs_info->block_max_order = calc_block_max_order(fs_info->sectorsize_bits);
fs_info->csums_per_leaf = BTRFS_MAX_ITEM_SIZE(fs_info) / fs_info->csum_size;
fs_info->stripesize = stripesize;
fs_info->fs_devices->fs_info = fs_info;