Hi Li,
On Thu, Feb 13, 2014 at 04:27:16PM +0800, Li Zefan wrote:
> On 2014/2/13 14:48, Brian Norris wrote:
> > On Wed, Feb 12, 2014 at 12:44:55PM -0800, Andrew Morton wrote:
> >> From: Li Zefan <lizefan@xxxxxxxxxx>
> >> Subject: jffs2: fix unbalanced locking
> >>
> >> This was found by our internal debugging feature on runtime, but this bug
> >> won't lead to deadlock, as the structure that this lock is embedded in is
> >> freed on error.
> >
> > Well, one of its callers frees it without unlocking it, but you're
> > forgetting about one of its other callers, and in doing so, you are
> > introducing a potential double-unlock instead!
>
> But I don't think I should be blamed here.
>
> Without my patch, some of the error paths release f->sem but some don't,
> so the potential double-unlock is already there.
So you can't be blamed for making *all* cases a double unlock? And this
patch is incorrect as well. See below.
> > BTW, the right way to handle lock balancing is to handle the unlocking
> > at the same level where you do the locking. So I guess you're looking
> > for the following patch instead, which is really not very useful because
> > (as Li noted) the lock is freed immediately afterward anyway:
> >
>
> Yeah, I do believe it's better to do locking/unlocking in the same level.
> How about this:
>
> [PATCH v2] jffs2: fix unbalanced locking
[...]
> diff --git a/fs/jffs2/readinode.c b/fs/jffs2/readinode.c
> index 386303d..6f22234 100644
> --- a/fs/jffs2/readinode.c
> +++ b/fs/jffs2/readinode.c
[...]
> @@ -1317,8 +1308,13 @@ static int jffs2_do_read_inode_internal(struct jffs2_sb_info *c,
> }
> if (f->inocache->state == INO_STATE_READING)
> jffs2_set_inocache_state(c, f->inocache, INO_STATE_PRESENT);
> -
> - return 0;
> +out:
> + if (ret) {
> + mutex_unlock(&f->sem);
> + jffs2_do_clear_inode(c, f);
> + mutex_lock(&f->sem);
This still is not consistent, and this access pattern (unlock / call
function which uses lock / lock) seems like a hack. How about we just
make the callers all do the same cleanup instead? Notice the 'error'
label in jffs2_iget(), which performs the jffs2_do_clear_inode() itself
already -- seemingly redundant. At least your patch doesn't add double
unlocks this time...
> + }
> + return ret;
> }
>
> /* Scan the list of all nodes present for this ino, build map of versions, etc. */
[...]
How about we just push all the mutex_unlock(&f->sem) and
jffs2_do_clear_inode() to the callers which hold the mutex? The
following patch is totally untested:
(BTW Li, have you actually tested any of your patches? I'm going to need
some Tested-by's before I merge any of this.)
Signed-off-by: Brian Norris <norris@xxxxxxxxxxxx>
diff --git a/fs/jffs2/fs.c b/fs/jffs2/fs.c
index a69e426435dd..9ac37354852d 100644
--- a/fs/jffs2/fs.c
+++ b/fs/jffs2/fs.c
@@ -272,12 +272,9 @@ struct inode *jffs2_iget(struct super_block *sb, unsigned long ino)
mutex_lock(&f->sem);
ret = jffs2_do_read_inode(c, f, inode->i_ino, &latest_node);
+ if (ret)
+ goto error;
- if (ret) {
- mutex_unlock(&f->sem);
- iget_failed(inode);
- return ERR_PTR(ret);
- }
inode->i_mode = jemode_to_cpu(latest_node.mode);
i_uid_write(inode, je16_to_cpu(latest_node.uid));
i_gid_write(inode, je16_to_cpu(latest_node.gid));
diff --git a/fs/jffs2/readinode.c b/fs/jffs2/readinode.c
index 386303dca382..5539ed46e89b 100644
--- a/fs/jffs2/readinode.c
+++ b/fs/jffs2/readinode.c
@@ -1203,17 +1203,13 @@ static int jffs2_do_read_inode_internal(struct jffs2_sb_info *c,
JFFS2_ERROR("failed to read from flash: error %d, %zd of %zd bytes read\n",
ret, retlen, sizeof(*latest_node));
/* FIXME: If this fails, there seems to be a memory leak. Find it. */
- mutex_unlock(&f->sem);
- jffs2_do_clear_inode(c, f);
- return ret?ret:-EIO;
+ return ret ? ret : -EIO;
}
crc = crc32(0, latest_node, sizeof(*latest_node)-8);
if (crc != je32_to_cpu(latest_node->node_crc)) {
JFFS2_ERROR("CRC failed for read_inode of inode %u at physical location 0x%x\n",
f->inocache->ino, ref_offset(rii.latest_ref));
- mutex_unlock(&f->sem);
- jffs2_do_clear_inode(c, f);
return -EIO;
}
@@ -1250,16 +1246,11 @@ static int jffs2_do_read_inode_internal(struct jffs2_sb_info *c,
* keep in RAM to facilitate quick follow symlink
* operation. */
uint32_t csize = je32_to_cpu(latest_node->csize);
- if (csize > JFFS2_MAX_NAME_LEN) {
- mutex_unlock(&f->sem);
- jffs2_do_clear_inode(c, f);
+ if (csize > JFFS2_MAX_NAME_LEN)
return -ENAMETOOLONG;
- }
f->target = kmalloc(csize + 1, GFP_KERNEL);
if (!f->target) {
JFFS2_ERROR("can't allocate %u bytes of memory for the symlink target path cache\n", csize);
- mutex_unlock(&f->sem);
- jffs2_do_clear_inode(c, f);
return -ENOMEM;
}
@@ -1271,8 +1262,6 @@ static int jffs2_do_read_inode_internal(struct jffs2_sb_info *c,
ret = -EIO;
kfree(f->target);
f->target = NULL;
- mutex_unlock(&f->sem);
- jffs2_do_clear_inode(c, f);
return ret;
}
@@ -1289,15 +1278,11 @@ static int jffs2_do_read_inode_internal(struct jffs2_sb_info *c,
if (f->metadata) {
JFFS2_ERROR("Argh. Special inode #%u with mode 0%o had metadata node\n",
f->inocache->ino, jemode_to_cpu(latest_node->mode));
- mutex_unlock(&f->sem);
- jffs2_do_clear_inode(c, f);
return -EIO;
}
if (!frag_first(&f->fragtree)) {
JFFS2_ERROR("Argh. Special inode #%u with mode 0%o has no fragments\n",
f->inocache->ino, jemode_to_cpu(latest_node->mode));
- mutex_unlock(&f->sem);
- jffs2_do_clear_inode(c, f);
return -EIO;
}
/* ASSERT: f->fraglist != NULL */
@@ -1305,8 +1290,6 @@ static int jffs2_do_read_inode_internal(struct jffs2_sb_info *c,
JFFS2_ERROR("Argh. Special inode #%u with mode 0x%x had more than one node\n",
f->inocache->ino, jemode_to_cpu(latest_node->mode));
/* FIXME: Deal with it - check crc32, check for duplicate node, check times and discard the older one */
- mutex_unlock(&f->sem);
- jffs2_do_clear_inode(c, f);
return -EIO;
}
/* OK. We're happy */
@@ -1400,10 +1383,8 @@ int jffs2_do_crccheck_inode(struct jffs2_sb_info *c, struct jffs2_inode_cache *i
f->inocache = ic;
ret = jffs2_do_read_inode_internal(c, f, &n);
- if (!ret) {
- mutex_unlock(&f->sem);
- jffs2_do_clear_inode(c, f);
- }
+ mutex_unlock(&f->sem);
+ jffs2_do_clear_inode(c, f);
jffs2_xattr_do_crccheck_inode(c, ic);
kfree (f);
return ret;
--
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