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Linux kernel stable tree
d48e1dea39
The purpose of btrfs_bbio_propagate_error() shall be propagating an error
of split bio to its original btrfs_bio, and tell the error to the upper
layer. However, it's not working well on some cases.
* Case 1. Immediate (or quick) end_bio with an error
When btrfs sends btrfs_bio to mirrored devices, btrfs calls
btrfs_bio_end_io() when all the mirroring bios are completed. If that
btrfs_bio was split, it is from btrfs_clone_bioset and its end_io function
is btrfs_orig_write_end_io. For this case, btrfs_bbio_propagate_error()
accesses the orig_bbio's bio context to increase the error count.
That works well in most cases. However, if the end_io is called enough
fast, orig_bbio's (remaining part after split) bio context may not be
properly set at that time. Since the bio context is set when the orig_bbio
(the last btrfs_bio) is sent to devices, that might be too late for earlier
split btrfs_bio's completion. That will result in NULL pointer
dereference.
That bug is easily reproducible by running btrfs/146 on zoned devices [1]
and it shows the following trace.
[1] You need raid-stripe-tree feature as it create "-d raid0 -m raid1" FS.
BUG: kernel NULL pointer dereference, address: 0000000000000020
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 1 UID: 0 PID: 13 Comm: kworker/u32:1 Not tainted 6.11.0-rc7-BTRFS-ZNS+ #474
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Workqueue: writeback wb_workfn (flush-btrfs-5)
RIP: 0010:btrfs_bio_end_io+0xae/0xc0 [btrfs]
BTRFS error (device dm-0): bdev /dev/mapper/error-test errs: wr 2, rd 0, flush 0, corrupt 0, gen 0
RSP: 0018:ffffc9000006f248 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff888005a7f080 RCX: ffffc9000006f1dc
RDX: 0000000000000000 RSI: 000000000000000a RDI: ffff888005a7f080
RBP: ffff888011dfc540 R08: 0000000000000000 R09: 0000000000000001
R10: ffffffff82e508e0 R11: 0000000000000005 R12: ffff88800ddfbe58
R13: ffff888005a7f080 R14: ffff888005a7f158 R15: ffff888005a7f158
FS: 0000000000000000(0000) GS:ffff88803ea80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000020 CR3: 0000000002e22006 CR4: 0000000000370ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
? __die_body.cold+0x19/0x26
? page_fault_oops+0x13e/0x2b0
? _printk+0x58/0x73
? do_user_addr_fault+0x5f/0x750
? exc_page_fault+0x76/0x240
? asm_exc_page_fault+0x22/0x30
? btrfs_bio_end_io+0xae/0xc0 [btrfs]
? btrfs_log_dev_io_error+0x7f/0x90 [btrfs]
btrfs_orig_write_end_io+0x51/0x90 [btrfs]
dm_submit_bio+0x5c2/0xa50 [dm_mod]
? find_held_lock+0x2b/0x80
? blk_try_enter_queue+0x90/0x1e0
__submit_bio+0xe0/0x130
? ktime_get+0x10a/0x160
? lockdep_hardirqs_on+0x74/0x100
submit_bio_noacct_nocheck+0x199/0x410
btrfs_submit_bio+0x7d/0x150 [btrfs]
btrfs_submit_chunk+0x1a1/0x6d0 [btrfs]
? lockdep_hardirqs_on+0x74/0x100
? __folio_start_writeback+0x10/0x2c0
btrfs_submit_bbio+0x1c/0x40 [btrfs]
submit_one_bio+0x44/0x60 [btrfs]
submit_extent_folio+0x13f/0x330 [btrfs]
? btrfs_set_range_writeback+0xa3/0xd0 [btrfs]
extent_writepage_io+0x18b/0x360 [btrfs]
extent_write_locked_range+0x17c/0x340 [btrfs]
? __pfx_end_bbio_data_write+0x10/0x10 [btrfs]
run_delalloc_cow+0x71/0xd0 [btrfs]
btrfs_run_delalloc_range+0x176/0x500 [btrfs]
? find_lock_delalloc_range+0x119/0x260 [btrfs]
writepage_delalloc+0x2ab/0x480 [btrfs]
extent_write_cache_pages+0x236/0x7d0 [btrfs]
btrfs_writepages+0x72/0x130 [btrfs]
do_writepages+0xd4/0x240
? find_held_lock+0x2b/0x80
? wbc_attach_and_unlock_inode+0x12c/0x290
? wbc_attach_and_unlock_inode+0x12c/0x290
__writeback_single_inode+0x5c/0x4c0
? do_raw_spin_unlock+0x49/0xb0
writeback_sb_inodes+0x22c/0x560
__writeback_inodes_wb+0x4c/0xe0
wb_writeback+0x1d6/0x3f0
wb_workfn+0x334/0x520
process_one_work+0x1ee/0x570
? lock_is_held_type+0xc6/0x130
worker_thread+0x1d1/0x3b0
? __pfx_worker_thread+0x10/0x10
kthread+0xee/0x120
? __pfx_kthread+0x10/0x10
ret_from_fork+0x30/0x50
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
Modules linked in: dm_mod btrfs blake2b_generic xor raid6_pq rapl
CR2: 0000000000000020
* Case 2. Earlier completion of orig_bbio for mirrored btrfs_bios
btrfs_bbio_propagate_error() assumes the end_io function for orig_bbio is
called last among split bios. In that case, btrfs_orig_write_end_io() sets
the bio->bi_status to BLK_STS_IOERR by seeing the bioc->error [2].
Otherwise, the increased orig_bio's bioc->error is not checked by anyone
and return BLK_STS_OK to the upper layer.
[2] Actually, this is not true. Because we only increases orig_bioc->errors
by max_errors, the condition "atomic_read(&bioc->error) > bioc->max_errors"
is still not met if only one split btrfs_bio fails.
* Case 3. Later completion of orig_bbio for un-mirrored btrfs_bios
In contrast to the above case, btrfs_bbio_propagate_error() is not working
well if un-mirrored orig_bbio is completed last. It sets
orig_bbio->bio.bi_status to the btrfs_bio's error. But, that is easily
over-written by orig_bbio's completion status. If the status is BLK_STS_OK,
the upper layer would not know the failure.
* Solution
Considering the above cases, we can only save the error status in the
orig_bbio (remaining part after split) itself as it is always
available. Also, the saved error status should be propagated when all the
split btrfs_bios are finished (i.e, bbio->pending_ios == 0).
This commit introduces "status" to btrfs_bbio and saves the first error of
split bios to original btrfs_bio's "status" variable. When all the split
bios are finished, the saved status is loaded into original btrfs_bio's
status.
With this commit, btrfs/146 on zoned devices does not hit the NULL pointer
dereference anymore.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.