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Date: Thu, 05 Feb 2015 15:30:47 -0600
From: Chris J Arges <chris.j.arges@...onical.com>
To: Omar Sandoval <osandov@...ndov.com>, Theodore Ts'o <tytso@....edu>,
Andreas Dilger <adilger.kernel@...ger.ca>,
Lukáš Czerner <lczerner@...hat.com>,
linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: fix indirect punch hole corruption
On 02/05/2015 02:50 PM, Omar Sandoval wrote:
> Commit 4f579ae7de56 (ext4: fix punch hole on files with indirect
> mapping) rewrote FALLOC_FL_PUNCH_HOLE for ext4 files with indirect
> mapping. However, the case where the punch happens within one level of
> indirection is incorrect. It assumes that the partial branches returned
> from ext4_find_shared will have the same depth, but this is not
> necessarily the case even when the offsets have the same depth. For
> example, if the last block occurs at the beginning of an indirect group
> (i.e., it has an offset of 0 at the end of the offsets array), then
> ext4_find_shared will return a shallower chain. So, let's handle the
> mismatch and clean up that case. Tested with generic/270, which no
> longer leads to an inconsistent filesystem like before.
>
> Signed-off-by: Omar Sandoval <osandov@...ndov.com>
Omar,
Tried running this with my original reproducer (qcow2 snapshotting and
rebooting) and got the following:
------------[ cut here ]------------
kernel BUG at fs/ext4/indirect.c:1488!
invalid opcode: 0000 [#1] SMP
<snip>
CPU: 4 PID: 9771 Comm: qemu-img Tainted: G W E
3.19.0-rc7-b164aa5 #22
Hardware name: XXX
task: ffff880243a34aa0 ti: ffff880240f3c000 task.ti: ffff880240f3c000
RIP: 0010:[<ffffffff812a38e7>] [<ffffffff812a38e7>]
ext4_ind_remove_space+0x737/0x740
RSP: 0018:ffff880240f3fc98 EFLAGS: 00010246
RAX: ffff880240f3fd98 RBX: ffff880240f3fd98 RCX: ffff880098c684dc
RDX: ffff880098c684d4 RSI: ffff880240f3fd08 RDI: ffff880098c684e0
RBP: ffff880240f3fdf8 R08: ffff880098c684e0 R09: 0000000000000000
R10: ffff880240f3faa0 R11: 0000000000000038 R12: ffff88009bb65810
R13: 0000000000000003 R14: ffff880240f3fd08 R15: ffff880240f3fd68
FS: 00007f7ad84ad700(0000) GS:ffff88024e500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7ae19a78ff CR3: 0000000241c52000 CR4: 00000000003427e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
ffffea0002596600 ffff88009bb65960 0000000000000050 0000000000000100
ffff8802447a2900 0000000000000003 ffff880240f3fd08 ffff88009b96c030
ffff880240f3fd08 000000000000024b 000000000000000d ffff880000000034
Call Trace:
[<ffffffff8129ccdc>] ? ext4_discard_preallocations+0x16c/0x480
[<ffffffff8126982f>] ext4_punch_hole+0x3bf/0x430
[<ffffffff81293c9e>] ext4_fallocate+0x16e/0x8c0
[<ffffffff811e4849>] ? __sb_start_write+0x49/0xf0
[<ffffffff811df3cf>] vfs_fallocate+0x12f/0x250
[<ffffffff810eda41>] ? SyS_futex+0x71/0x150
[<ffffffff811e0408>] SyS_fallocate+0x48/0x80
[<ffffffff8177cc2d>] system_call_fastpath+0x16/0x1b
Code: 40 4c 8d 0c c5 e8 ff ff ff 49 c1 f9 03 45 69 c9 ab aa aa aa e8 6b
e2 ff ff 48 8b 85 10 ff ff ff c7 00 00 00 00 00 e9 fd fa ff ff <0f> 0b
0f 0b 0f 1f 44 00 00 0f 1f 44 00 00 55 48 89 e5 41 56 41
RIP [<ffffffff812a38e7>] ext4_ind_remove_space+0x737/0x740
RSP <ffff880240f3fc98>
---[ end trace 05f053fdd5d908a8 ]---
So this is hitting the BUG_ON you added.
--chris
> ---
> fs/ext4/indirect.c | 61 +++++++++++++++++++++++++++++++-----------------------
> 1 file changed, 35 insertions(+), 26 deletions(-)
>
> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
> index 36b3696..e04bbce 100644
> --- a/fs/ext4/indirect.c
> +++ b/fs/ext4/indirect.c
> @@ -1434,50 +1434,59 @@ end_range:
> * in punch_hole so we need to point to the next element
> */
> partial2->p++;
> - while ((partial > chain) || (partial2 > chain2)) {
> - /* We're at the same block, so we're almost finished */
> - if ((partial->bh && partial2->bh) &&
> - (partial->bh->b_blocknr == partial2->bh->b_blocknr)) {
> - if ((partial > chain) && (partial2 > chain2)) {
> - ext4_free_branches(handle, inode, partial->bh,
> - partial->p + 1,
> - partial2->p,
> - (chain+n-1) - partial);
> - BUFFER_TRACE(partial->bh, "call brelse");
> - brelse(partial->bh);
> - BUFFER_TRACE(partial2->bh, "call brelse");
> - brelse(partial2->bh);
> - }
> + while (partial > chain && partial2 > chain2) {
> + int depth = (chain+n-1) - partial;
> + int depth2 = (chain2+n2-1) - partial2;
> +
> + if (partial->bh->b_blocknr == partial2->bh->b_blocknr) {
> + /*
> + * We've converged on the same block. Clear the range,
> + * then we're done.
> + */
> + ext4_free_branches(handle, inode, partial->bh,
> + partial->p + 1,
> + partial2->p,
> + (chain+n-1) - partial);
> + BUFFER_TRACE(partial->bh, "call brelse");
> + brelse(partial->bh);
> + BUFFER_TRACE(partial2->bh, "call brelse");
> + brelse(partial2->bh);
> return 0;
> }
> +
> /*
> - * Clear the ends of indirect blocks on the shared branch
> - * at the start of the range
> + * The start and end partial branches may not be at the same
> + * level even though the punch happened within one level. So, we
> + * give them a chance to arrive at the same level, then walk
> + * them in step with each other until we converge on the same
> + * block.
> */
> - if (partial > chain) {
> + if (depth <= depth2) {
> ext4_free_branches(handle, inode, partial->bh,
> - partial->p + 1,
> - (__le32 *)partial->bh->b_data+addr_per_block,
> - (chain+n-1) - partial);
> + partial->p + 1,
> + (__le32 *)partial->bh->b_data+addr_per_block,
> + (chain+n-1) - partial);
> BUFFER_TRACE(partial->bh, "call brelse");
> brelse(partial->bh);
> partial--;
> }
> - /*
> - * Clear the ends of indirect blocks on the shared branch
> - * at the end of the range
> - */
> - if (partial2 > chain2) {
> + if (depth2 <= depth) {
> ext4_free_branches(handle, inode, partial2->bh,
> (__le32 *)partial2->bh->b_data,
> partial2->p,
> - (chain2+n-1) - partial2);
> + (chain2+n2-1) - partial2);
> BUFFER_TRACE(partial2->bh, "call brelse");
> brelse(partial2->bh);
> partial2--;
> }
> }
>
> + /*
> + * The punch happened within the same level, so at some point we _must_
> + * converge on an indirect block.
> + */
> + BUG_ON(1);
> +
> do_indirects:
> /* Kill the remaining (whole) subtrees */
> switch (offsets[0]) {
>
--
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