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&gt; wrote: > > Hi Tao, > > On Sat, 18 Sep 2021 15:59:32 +0800 > Tao Liu <ltao(a)redhat.com&gt; 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&gt; > > --- > > 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 >