Re: [Crash-utility] [PATCH v4 4/4] Add check if an syment element is installed one more time
Hi Philipp,
Thanks for reviewing the patch!
On Thu, Sep 23, 2021 at 8:19 PM Philipp Rudo <prudo(a)redhat.com> wrote:
Hi Tao,
On Sat, 18 Sep 2021 15:59:32 +0800
Tao Liu <ltao(a)redhat.com> wrote:
> symname_hash_install won't check if spn has been installed before. If
> it does, the second install will corrupt the hash table as well as
> spn->cnt counting. This patch adds the check to avoid such risks.
>
> Signed-off-by: Tao Liu <ltao(a)redhat.com>
> ---
> symbols.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/symbols.c b/symbols.c
> index f7157b1..6d12c55 100644
> --- a/symbols.c
> +++ b/symbols.c
> @@ -1147,6 +1147,20 @@ mod_symtable_hash_remove_range(struct syment *from, struct
syment *to)
> symname_hash_remove(st->mod_symname_hash, sp);
> }
>
> +static inline int
> +syment_is_installed(struct syment *table[], struct syment *spn)
> +{
> + struct syment *sp;
> + int index;
> +
> + index = SYMNAME_HASH_INDEX(spn->name);
> + for (sp = table[index]; sp; sp = sp->name_hash_next) {
> + if (sp == spn)
> + return TRUE;
> + }
> + return FALSE;
> +}
> +
> /*
> * Install a single static kernel symbol into the symname_hash.
> */
> @@ -1156,7 +1170,7 @@ symname_hash_install(struct syment *table[], struct syment
*spn)
> struct syment *sp;
> int index;
>
> - if (!spn)
> + if (!spn || syment_is_installed(table, spn))
> return;
>
> index = SYMNAME_HASH_INDEX(spn->name);
hmm... not sure if this is a little bit over the top. The idea I had
was in your v3 simply replace
assert(sp != spn);
by
if (sp == spn) {
error(WARNING, "Symbol %s already installed in symname_hash\n",
sp->name);
continue;
}
It may not be easy to replace with "check if sp == spn and continue".
For example, if we already have
3 syments installed, which all have the same name, such as
(sp1{cnt == 3, name == "str"}, sp2{cnt == 3, name == "str"}, sp3{cnt
== 3, name == "str"})
in the hashtable, and we will install sp3 again(sp3 == spn) into the hashtable.
The cnt will get increased for sp1 and sp2 in the following code:
while (sp) {
if (sp == spn) {
error(....);
continue;
}
if (STREQ(sp->name, spn->name)) {
sp->cnt++;
spn->cnt++;
}
.....
}
However, when iteration reaches sp3, it will not increase cnt and not
install spn. Thus we will have
(sp1{cnt == 4}, sp2{cnt == 4}, sp3{cnt == 3}) in the hashtable, cnt
gets corrupted. In other words,
we need to revert all the previous cnt++ when we reach sp == spn. It
will require
more code to implement the 'revert' operation, and it is not as clear
as syment_is_installed
check.
That's less code plus the warning makes it easier to detect that
there
is a problem (for me the case sp == spn is a sign for a bug in crash).
What do you think?
From my point,
1) assert() check: Use least code, simple and
clear, but too strict.
2) syment_is_installed check: Use more code, clear, acceptable to me.
3) introduce 'cnt++ revert' operation: I haven't think of a better way, from
the current inspection, it uses more code, and is not elegant.
What do you think?
Thanks,
Tao Liu
Thanks
Philipp