* Is there any reason for us to use EXT4_MAXQUOTAS_INIT_BLOCKS?
@ 2015-04-15 15:55 Theodore Ts'o
2015-04-15 20:47 ` Jan Kara
0 siblings, 1 reply; 3+ messages in thread
From: Theodore Ts'o @ 2015-04-15 15:55 UTC (permalink / raw)
To: Jan Kara; +Cc: linux-ext4
It looks to me like EXT4_MAXQUOTAS_INIT_BLOCKS includes the credits
neede to set up the quota records. So if we move the call to
dquot_initialize(inode) outside of the normal transaction (which we
should probably do in all cases), that means that we shouldn't ever
need to use EXT4_MAX_QUOTAS_INIT_BLOCKS. Is that right?
The reason why I ask is the following is a easy way to trigger a file
system problem:
mke2fs -Fq -t ext4 -b 4096 /dev/vdc 50M
mount -t ext4 -o usrquota,grpquota /dev/vdc
l8=12345678
l16=$l8$l8
l32=$l16$l16
l64=$l32$l32
dmesg -n 7
ln -s $l64 /vdc/link
This will result in:
[ 5.229165] JBD2: ln wants too many credits (156 > 128)
[ 5.230194] EXT4-fs error (device vdc) in __ext4_new_inode:843: error 28
In other places where we are allocating a new inode (such as mknod),
we're doing the following:
credits = EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +
EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3;
Which is 37 blocks, and I suspect that's still too darned much. But
if we don't need to use EXT4_MAXQUOTAS_INIT_BLOCKS in ext4_mknod(), we
shouldn't be needing it in ext4_symlink(), either.
Am I missing anything?
Thanks,
- Ted
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Is there any reason for us to use EXT4_MAXQUOTAS_INIT_BLOCKS?
2015-04-15 15:55 Is there any reason for us to use EXT4_MAXQUOTAS_INIT_BLOCKS? Theodore Ts'o
@ 2015-04-15 20:47 ` Jan Kara
2015-04-15 23:27 ` Theodore Ts'o
0 siblings, 1 reply; 3+ messages in thread
From: Jan Kara @ 2015-04-15 20:47 UTC (permalink / raw)
To: Theodore Ts'o; +Cc: Jan Kara, linux-ext4
On Wed 15-04-15 11:55:37, Ted Tso wrote:
> It looks to me like EXT4_MAXQUOTAS_INIT_BLOCKS includes the credits
> neede to set up the quota records. So if we move the call to
> dquot_initialize(inode) outside of the normal transaction (which we
> should probably do in all cases), that means that we shouldn't ever
> need to use EXT4_MAX_QUOTAS_INIT_BLOCKS. Is that right?
Correct. EXT4_MAX_QUOTAS_INIT_BLOCKS is only needed if we create the
first file for a user. So chown / chgrp may need this and inode creation
may need this. As you say, if dquot_init() is in a separate transaction,
then inode creation has to account only for a standard quota operation.
> The reason why I ask is the following is a easy way to trigger a file
> system problem:
>
> mke2fs -Fq -t ext4 -b 4096 /dev/vdc 50M
> mount -t ext4 -o usrquota,grpquota /dev/vdc
> l8=12345678
> l16=$l8$l8
> l32=$l16$l16
> l64=$l32$l32
> dmesg -n 7
> ln -s $l64 /vdc/link
>
> This will result in:
>
> [ 5.229165] JBD2: ln wants too many credits (156 > 128)
> [ 5.230194] EXT4-fs error (device vdc) in __ext4_new_inode:843: error 28
>
> In other places where we are allocating a new inode (such as mknod),
> we're doing the following:
>
> credits = EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +
> EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3;
>
> Which is 37 blocks, and I suspect that's still too darned much. But
> if we don't need to use EXT4_MAXQUOTAS_INIT_BLOCKS in ext4_mknod(), we
> shouldn't be needing it in ext4_symlink(), either.
>
> Am I missing anything?
Yeah, the credit estimate in ext4_symlink():
credits = 4 + EXT4_MAXQUOTAS_INIT_BLOCKS(dir->i_sb) + EXT4_XATTR_TRANS_BLOCKS;
is just too pessimistic. Actually what we need for long symlinks is only
credits for inode creation + addition to orphan list (so 4 +
EXT4_MAXQUOTAS_TRANS_BLOCKS -- sb, gdt, bitmap, inode). Then we stop the
transaction and add block to the symlink in a separate transaction. And
then we link symlink into a directory in yet another transaction.
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Is there any reason for us to use EXT4_MAXQUOTAS_INIT_BLOCKS?
2015-04-15 20:47 ` Jan Kara
@ 2015-04-15 23:27 ` Theodore Ts'o
0 siblings, 0 replies; 3+ messages in thread
From: Theodore Ts'o @ 2015-04-15 23:27 UTC (permalink / raw)
To: Jan Kara; +Cc: linux-ext4
On Wed, Apr 15, 2015 at 10:47:54PM +0200, Jan Kara wrote:
> Yeah, the credit estimate in ext4_symlink():
> credits = 4 + EXT4_MAXQUOTAS_INIT_BLOCKS(dir->i_sb) + EXT4_XATTR_TRANS_BLOCKS;
> is just too pessimistic. Actually what we need for long symlinks is only
> credits for inode creation + addition to orphan list (so 4 +
> EXT4_MAXQUOTAS_TRANS_BLOCKS -- sb, gdt, bitmap, inode).
Thanks, I just wanted to check with you before I fixed this, since we
didn't have anything explicitly documenting what
EXT4_MAXQUOAS_INIT_BLOCKS did (which I'll fix as well while I'm at
it), and I didn't want to make anything assumptions that might come
back and bite us later. Of course, the fact that ext4_symlinks was
using way more credits than ext4_mknod made it clear something was
buggy, and I couldn't imagine any circumstances why creating a long
symlink (or more correctly, only the first part of creatinga long
symlink) would require modifying 156 metadata blocks! :-)
- Ted
^ permalink raw reply [flat|nested] 3+ messages in thread
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2015-04-15 15:55 Is there any reason for us to use EXT4_MAXQUOTAS_INIT_BLOCKS? Theodore Ts'o
2015-04-15 20:47 ` Jan Kara
2015-04-15 23:27 ` Theodore Ts'o
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