On 22/02/01 12:21PM, Jan Kara wrote:
> On Mon 31-01-22 20:46:50, Ritesh Harjani wrote:
> > In case of flex_bg feature (which is by default enabled), extents for
> > any given inode might span across blocks from two different block group.
> > ext4_mb_mark_bb() only reads the buffer_head of block bitmap once for the
> > starting block group, but it fails to read it again when the extent length
> > boundary overflows to another block group. Then in this below loop it
> > accesses memory beyond the block group bitmap buffer_head and results
> > into a data abort.
> >
> > for (i = 0; i < clen; i++)
> > if (!mb_test_bit(blkoff + i, bitmap_bh->b_data) == !state)
> > already++;
> >
> > This patch adds this functionality for checking block group boundary in
> > ext4_mb_mark_bb() and update the buffer_head(bitmap_bh) for every different
> > block group.
> >
> > w/o this patch, I was easily able to hit a data access abort using Power platform.
> >
> > <...>
> > [ 74.327662] EXT4-fs error (device loop3): ext4_mb_generate_buddy:1141: group 11, block bitmap and bg descriptor inconsistent: 21248 vs 23294 free clusters
> > [ 74.533214] EXT4-fs (loop3): shut down requested (2)
> > [ 74.536705] Aborting journal on device loop3-8.
> > [ 74.702705] BUG: Unable to handle kernel data access on read at 0xc00000005e980000
> > [ 74.703727] Faulting instruction address: 0xc0000000007bffb8
> > cpu 0xd: Vector: 300 (Data Access) at [c000000015db7060]
> > pc: c0000000007bffb8: ext4_mb_mark_bb+0x198/0x5a0
> > lr: c0000000007bfeec: ext4_mb_mark_bb+0xcc/0x5a0
> > sp: c000000015db7300
> > msr: 800000000280b033
> > dar: c00000005e980000
> > dsisr: 40000000
> > current = 0xc000000027af6880
> > paca = 0xc00000003ffd5200 irqmask: 0x03 irq_happened: 0x01
> > pid = 5167, comm = mount
> > <...>
> > enter ? for help
> > [c000000015db7380] c000000000782708 ext4_ext_clear_bb+0x378/0x410
> > [c000000015db7400] c000000000813f14 ext4_fc_replay+0x1794/0x2000
> > [c000000015db7580] c000000000833f7c do_one_pass+0xe9c/0x12a0
> > [c000000015db7710] c000000000834504 jbd2_journal_recover+0x184/0x2d0
> > [c000000015db77c0] c000000000841398 jbd2_journal_load+0x188/0x4a0
> > [c000000015db7880] c000000000804de8 ext4_fill_super+0x2638/0x3e10
> > [c000000015db7a40] c0000000005f8404 get_tree_bdev+0x2b4/0x350
> > [c000000015db7ae0] c0000000007ef058 ext4_get_tree+0x28/0x40
> > [c000000015db7b00] c0000000005f6344 vfs_get_tree+0x44/0x100
> > [c000000015db7b70] c00000000063c408 path_mount+0xdd8/0xe70
> > [c000000015db7c40] c00000000063c8f0 sys_mount+0x450/0x550
> > [c000000015db7d50] c000000000035770 system_call_exception+0x4a0/0x4e0
> > [c000000015db7e10] c00000000000c74c system_call_common+0xec/0x250
> > --- Exception: c00 (System Call) at 00007ffff7dbfaa4
> >
> > Fixes: 8016e29f4362e28 ("ext4: fast commit recovery path")
> > Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
> > ---
> > fs/ext4/mballoc.c | 30 +++++++++++++++++++++++++++---
> > 1 file changed, 27 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index c781974df9d0..8d23108cf9d7 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -3899,12 +3899,29 @@ void ext4_mb_mark_bb(struct super_block *sb, ext4_fsblk_t block,
> > struct ext4_sb_info *sbi = EXT4_SB(sb);
> > ext4_group_t group;
> > ext4_grpblk_t blkoff;
> > - int i, clen, err;
> > + int i, err;
> > int already;
> > + unsigned int clen, overflow;
> >
> > - clen = EXT4_B2C(sbi, len);
> > -
> > +again:
>
> And maybe structure this as a while loop? Like:
>
> while (len > 0) {
> ...
> }
Sure, will check.
>
> > + overflow = 0;
> > ext4_get_group_no_and_offset(sb, block, &group, &blkoff);
> > +
> > + /*
> > + * Check to see if we are freeing blocks across a group
> > + * boundary.
> > + * In case of flex_bg, this can happen that (block, len) may span across
> > + * more than one group. In that case we need to get the corresponding
> > + * group metadata to work with. For this we have goto again loop.
> > + */
> > + if (EXT4_C2B(sbi, blkoff) + len > EXT4_BLOCKS_PER_GROUP(sb)) {
> > + overflow = EXT4_C2B(sbi, blkoff) + len -
> > + EXT4_BLOCKS_PER_GROUP(sb);
> > + len -= overflow;
>
> Why not just:
>
> thisgrp_len = min_t(int, len,
> EXT4_BLOCKS_PER_GROUP(sb) - EXT4_C2B(sbi, blkoff));
> clen = EXT4_NUM_B2C(sbi, thisgrp_len);
>
> It seems easier to understand to me.
Agree, will make this change.
-ritesh
