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Date: Thu, 06 Nov 2008 15:28:10 -0800
From: Mingming Cao <cmm@...ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: jack@...e.cz, tytso@....edu, linux-ext4@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V2 1/3] quota: Add reservation support for delayed
block allocation
On Tue, 2008-11-04 at 17:14 -0800, Andrew Morton wrote:
> On Fri, 31 Oct 2008 14:27:22 -0700
> Mingming Cao <cmm@...ibm.com> wrote:
>
> > +int dquot_alloc_space(struct inode *inode, qsize_t number, int warn)
> > +{
> > + int cnt, ret = QUOTA_OK;
> > +
> > + /*
> > + * First test before acquiring mutex - solves deadlocks when we
> > + * re-enter the quota code and are already holding the mutex
> > + */
> > + if (IS_NOQUOTA(inode)) {
> > + inode_add_bytes(inode, number);
> > + return ret;
> > + }
> > +
> > + down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
> > + if (IS_NOQUOTA(inode)) {
> > + /* Now we can do reliable test... */
> > + up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
> > + inode_add_bytes(inode, number);
> > + return ret;
> > + }
> > +
> > + ret = __dquot_alloc_space(inode, number, warn, 0);
> > + if (ret == NO_QUOTA) {
> > + up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
> > + return ret;
> > + }
> > +
> > + /* Dirtify all the dquots - this can block when journalling */
> > + for (cnt = 0; cnt < MAXQUOTAS; cnt++)
> > + if (inode->i_dquot[cnt])
> > + mark_dquot_dirty(inode->i_dquot[cnt]);
> > + up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
> > + inode_add_bytes(inode, number);
> > + return ret;
> > +}
>
> I'm going to have to call "ug" on that code.
>
> Multiple return points per function really is a maintenance problem.
> It's a great source of code duplication, locking errors and resource
> leaks as the code evolves.
>
> Can we please rework this code (and any other similar code here) to use
> the usual `goto out' pattern?
>
>
Ok, I was following the same style in the quota code, but I will do
that.
> int dquot_alloc_space(struct inode *inode, qsize_t number, int warn)
> {
> int cnt, ret = QUOTA_OK;
>
> /*
> * First test before acquiring mutex - solves deadlocks when we
> * re-enter the quota code and are already holding the mutex
> */
> if (IS_NOQUOTA(inode))
> goto out;
>
> down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
> if (IS_NOQUOTA(inode)) /* Now we can do reliable test... */
> goto out_unlock;
>
> ret = __dquot_alloc_space(inode, number, warn, 0);
>
> if (ret == NO_QUOTA) {
> up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
> return ret;
> }
>
> <<
>
> I don't know what to do here - did we really want to skip the
> inode_add_bytes?
Yes, this is the failure case. In case the request exceeds the quota
limit, we will quit with error without block allocation, so the inode
bytes update should be skipped.
> If so, we could do
>
> number = 0;
> goto out_unlock;
>
> >>
>
> /* Dirtify all the dquots - this can block when journalling */
> for (cnt = 0; cnt < MAXQUOTAS; cnt++)
> if (inode->i_dquot[cnt])
> mark_dquot_dirty(inode->i_dquot[cnt]);
> out_unlock:
> up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
> out:
> inode_add_bytes(inode, number);
> return ret;
> }
>
> or something like that.
>
>
Attached is the incremental fixes. I will post the updated series
later.
Thanks,
---
fs/dquot.c | 40 +++++++++++++++++-----------------------
include/linux/quotaops.h | 2 +-
2 files changed, 18 insertions(+), 24 deletions(-)
Index: linux-2.6.28-rc2/fs/dquot.c
===================================================================
--- linux-2.6.28-rc2.orig/fs/dquot.c 2008-11-06 12:28:22.000000000 -0800
+++ linux-2.6.28-rc2/fs/dquot.c 2008-11-06 12:49:07.000000000 -0800
@@ -1276,33 +1276,28 @@ int dquot_alloc_space(struct inode *inod
/*
* First test before acquiring mutex - solves deadlocks when we
- * re-enter the quota code and are already holding the mutex
- */
- if (IS_NOQUOTA(inode)) {
- inode_add_bytes(inode, number);
- return ret;
- }
+ * re-enter the quota code and are already holding the mutex
+ */
+ if (IS_NOQUOTA(inode))
+ goto out;
down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
- if (IS_NOQUOTA(inode)) {
- /* Now we can do reliable test... */
- up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
- inode_add_bytes(inode, number);
- return ret;
- }
+ if (IS_NOQUOTA(inode))
+ goto out_unlock;
ret = __dquot_alloc_space(inode, number, warn, 0);
- if (ret == NO_QUOTA) {
- up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
- return ret;
- }
+ if (ret == NO_QUOTA)
+ goto out_unlock;
/* Dirtify all the dquots - this can block when journalling */
for (cnt = 0; cnt < MAXQUOTAS; cnt++)
if (inode->i_dquot[cnt])
mark_dquot_dirty(inode->i_dquot[cnt]);
+out_unlock:
up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
- inode_add_bytes(inode, number);
+out:
+ if (ret == QUOTA_OK)
+ inode_add_bytes(inode, number);
return ret;
}
@@ -1311,17 +1306,16 @@ int dquot_reserve_space(struct inode *in
int ret = QUOTA_OK;
if (IS_NOQUOTA(inode))
- return ret;
+ goto out;
down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
- if (IS_NOQUOTA(inode)) {
- /* Now we can do reliable test... */
- up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
- return ret;
- }
+ if (IS_NOQUOTA(inode))
+ goto out_unlock;
ret = __dquot_alloc_space(inode, number, warn, 1);
+out_unlock:
up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
+out:
return ret;
}
Index: linux-2.6.28-rc2/include/linux/quotaops.h
===================================================================
--- linux-2.6.28-rc2.orig/include/linux/quotaops.h 2008-11-06 12:28:22.000000000 -0800
+++ linux-2.6.28-rc2/include/linux/quotaops.h 2008-11-06 12:48:24.000000000 -0800
@@ -383,7 +383,7 @@ static inline int vfs_dq_alloc_block(str
static inline int vfs_dq_reserve_block(struct inode *inode, qsize_t nr)
{
return vfs_dq_reserve_space(inode,
- nr << inode->i_sb->s_blocksize_bits);
+ nr << inode->i_blkbits);
}
static inline void vfs_dq_free_block_nodirty(struct inode *inode, qsize_t nr)
--
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