Sergio Gutierrez wrote:
> Hi Henning.
>
> I apologize in advance for the long post.
>
> These days, Openser still has been crashing randomly.
>
> Using GDB in one of the generated core files, I found something curious:
>
> #0 0x000bcfbc in fm_malloc (qm=0x185320, size=24, file=0xfedbac10
> "res.c",
> func=0xfedbac70 "db_mysql_get_columns", line=62) at mem/f_malloc.c:267
> #1 0xfedb74b0 in db_mysql_get_columns (_h=0x1cbf68, _r=0x24dde8) at
> res.c:62
> #2 0xfedb79f0 in db_mysql_convert_result (_h=0x1cbf68, _r=0x24dde8)
> at res.c:167
> #3 0xfedb28c4 in db_mysql_store_result (_h=0x1cbf68, _r=0xffbff830)
> at dbase.c:209
> #4 0xfedb40e8 in db_mysql_raw_query (_h=0x1cbf68,
> _s=0xff07e668 "select received, contact, socket, cflags, path from
> location where expires > '2008-03-04 13:37:51' and cflags & 64 = 64
> and id % 1 = 0", _r=0xffbff830) at dbase.c:447
> #5 0xff053260 in get_all_db_ucontacts (buf=0x1ceec0, len=320054,
> flags=64, part_idx=0, part_max=1)
> at dlist.c:128
> #6 0xff0528c8 in get_all_ucontacts (buf=0x1ceec0, len=320058,
> flags=64, part_idx=0, part_max=1) at dlist.c:356
> #7 0xfee57c6c in pingClients (ticks=60, param=0x0) at functions.h:60
> #8 0x000aa430 in timer_ticker (timer_list=0x163c00) at timer.c:275
> #9 0x000aa180 in run_timer_process (tpl=0x1c5808, do_jiffies=1) at
> timer.c:357
> #10 0x000aa6fc in start_timer_processes () at timer.c:386
> #11 0x00036788 in main_loop () at main.c:873
> #12 0x0003a0c4 in main (argc=1137536, argv=0x155f1c) at main.c:1372
>
> By inspecting in detail the frame 0, in particular the qm variable:
>
> (gdb) print qm
> $1 = (struct fm_block *) 0x185320
>
>
> Which is the fm_block structure defined at mem/f_malloc.h.
>
> (gdb) frame 0
> #0 0x000bcfbc in fm_malloc (qm=0x185320, size=24, file=0xfedbac10
> "res.c",
> func=0xfedbac70 "db_mysql_get_columns", line=62) at mem/f_malloc.c:267
> 267 if ((*f)->size>=size) goto found;
> (gdb) list
> 262 /*search for a suitable free frag*/
> 263
> 264 for(hash=GET_HASH(size);hash<F_HASH_SIZE;hash++){
> 265 f=&(qm->free_hash[hash].first);
> 266 for(;(*f); f=&((*f)->u.nxt_free))
> 267 if ((*f)->size>=size) goto found;
> 268 /* try in a bigger bucket */
> 269 }
> 270 /* not found, bad! */
> 271 return 0;
>
>
> If I print the qm->free_hash array, I found that is mainly empty; For
> the particular case of my core file, hash has a value of three, when
> printing that position I have the following:
>
> (gdb) print qm->free_hash[hash]
> $1 = {first = 0x69703a31, no = 1}
> (gdb) print qm->free_hash
> $2 = {{first = 0x0, no = 0}, {first = 0x0, no = 0}, {first = 0x0, no =
> 0}, {first = 0x69703a31, no = 1}, {
> first = 0x0, no = 0}, {first = 0x0, no = 0}, {first = 0x0, no =
> 0}, {first = 0x0, no = 0}, {first = 0x0,
> no = 0}, {first = 0x0, no = 0}, {first = 0x24dd68, no = 4641},
> {first = 0x0, no = 0} <repeats 21 times>, {
> first = 0x1ced90, no = 1}, {first = 0x0, no = 0} <repeats 679
> times>, {first = 0x1cef40, no = 1}, {
> first = 0x0, no = 0} <repeats 1337 times>, {first = 0x1cef40, no =
> 1}, {first = 0x0, no = 0}, {
> first = 0x24de38, no = 1}, {first = 0x0, no = 0} <repeats 11
> times>, {first = 0x21d100, no = 1}, {
> first = 0x0, no = 0}, {first = 0x0, no = 0}}
> (gdb) print qm->free_hash.no
> $3 = 0
> (gdb) print qm->free_hash[hash].first
> $4 = (struct fm_frag *) 0x69703a31
> (gdb) x/s 0x69703a31
> 0x69703a31: <Address 0x69703a31 out of bounds>
>
>
> So, the error happened because from the list of memory fragments, an
> invalid one was referred.
>
> I have two questions:
>
> 1. Is it normal that free_hash array at fm_block has some positions
> pointing to invalid locations?
> 2. I could see that the fm_frag_lnk struct has a member called no,
> which, for the printing, I see it is 0 for most of the values at the
> array, and it is 1 at some members, including the one which causes the
> crash; would it not be possible to use that member for a check before
> trying the allocation? What exactly means the no member, as I also see
> that for some of the members it has a value higher than 1.
>
> Thanks in advance for any help, and again, I apologize for the long post.
>
> Best regards.
>
> Sergio Gutierrez
>
>
> On Thu, Feb 28, 2008 at 11:49 AM, Sergio Gutierrez <
saguti@gmail.com