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7f03a417fc
[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>
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