fs/btrfs/bio.c | 37 +++++++++++++------------------------ fs/btrfs/bio.h | 3 +++ 2 files changed, 16 insertions(+), 24 deletions(-)
The patch below does not apply to the v6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.
Thanks,
Sasha
------------------ original commit in Linus's tree ------------------
From d48e1dea3931de64c26717adc2b89743c7ab6594 Mon Sep 17 00:00:00 2001
From: Naohiro Aota <naohiro.aota@wdc.com>
Date: Wed, 9 Oct 2024 22:52:06 +0900
Subject: [PATCH] btrfs: fix error propagation of split bios
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: 852eee62d31a ("btrfs: allow btrfs_submit_bio to split bios")
CC: stable@vger.kernel.org # 6.6+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/bio.c | 37 +++++++++++++------------------------
fs/btrfs/bio.h | 3 +++
2 files changed, 16 insertions(+), 24 deletions(-)
diff --git a/fs/btrfs/bio.c b/fs/btrfs/bio.c
index ce13416bc10f0..f83ec5a1baa60 100644
--- a/fs/btrfs/bio.c
+++ b/fs/btrfs/bio.c
@@ -49,6 +49,7 @@ void btrfs_bio_init(struct btrfs_bio *bbio, struct btrfs_fs_info *fs_info,
bbio->end_io = end_io;
bbio->private = private;
atomic_set(&bbio->pending_ios, 1);
+ WRITE_ONCE(bbio->status, BLK_STS_OK);
}
/*
@@ -120,41 +121,29 @@ static void __btrfs_bio_end_io(struct btrfs_bio *bbio)
}
}
-static void btrfs_orig_write_end_io(struct bio *bio);
-
-static void btrfs_bbio_propagate_error(struct btrfs_bio *bbio,
- struct btrfs_bio *orig_bbio)
-{
- /*
- * For writes we tolerate nr_mirrors - 1 write failures, so we can't
- * just blindly propagate a write failure here. Instead increment the
- * error count in the original I/O context so that it is guaranteed to
- * be larger than the error tolerance.
- */
- if (bbio->bio.bi_end_io == &btrfs_orig_write_end_io) {
- struct btrfs_io_stripe *orig_stripe = orig_bbio->bio.bi_private;
- struct btrfs_io_context *orig_bioc = orig_stripe->bioc;
-
- atomic_add(orig_bioc->max_errors, &orig_bioc->error);
- } else {
- orig_bbio->bio.bi_status = bbio->bio.bi_status;
- }
-}
-
void btrfs_bio_end_io(struct btrfs_bio *bbio, blk_status_t status)
{
bbio->bio.bi_status = status;
if (bbio->bio.bi_pool == &btrfs_clone_bioset) {
struct btrfs_bio *orig_bbio = bbio->private;
- if (bbio->bio.bi_status)
- btrfs_bbio_propagate_error(bbio, orig_bbio);
btrfs_cleanup_bio(bbio);
bbio = orig_bbio;
}
- if (atomic_dec_and_test(&bbio->pending_ios))
+ /*
+ * At this point, bbio always points to the original btrfs_bio. Save
+ * the first error in it.
+ */
+ if (status != BLK_STS_OK)
+ cmpxchg(&bbio->status, BLK_STS_OK, status);
+
+ if (atomic_dec_and_test(&bbio->pending_ios)) {
+ /* Load split bio's error which might be set above. */
+ if (status == BLK_STS_OK)
+ bbio->bio.bi_status = READ_ONCE(bbio->status);
__btrfs_bio_end_io(bbio);
+ }
}
static int next_repair_mirror(struct btrfs_failed_bio *fbio, int cur_mirror)
diff --git a/fs/btrfs/bio.h b/fs/btrfs/bio.h
index e486123407458..e2fe16074ad65 100644
--- a/fs/btrfs/bio.h
+++ b/fs/btrfs/bio.h
@@ -79,6 +79,9 @@ struct btrfs_bio {
/* File system that this I/O operates on. */
struct btrfs_fs_info *fs_info;
+ /* Save the first error status of split bio. */
+ blk_status_t status;
+
/*
* This member must come last, bio_alloc_bioset will allocate enough
* bytes for entire btrfs_bio but relies on bio being last.
--
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