Re: [Tarantool-patches] [PATCH luajit 2/3] core: fix resources leak in memory profiler

[Sergey Ostanevich <sergos@tarantool.org>]

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Serge, can you point me to a branch please?

> On 30 Dec 2020, at 12:06, Igor Munkin <imun@tarantool.org> wrote:
> 
> Sergey,
> 
> Thanks for the patch! LGTM except the wording in commit message
> (consider the comments below).
> 
> Side note: I want to notice that with on_start callback things would be
> clearer. Let's return to this again later.
> 
> On 30.12.20, Sergey Kaplun wrote:
>> When the profiler is failing to start with error different from
> 
> Typo: s/is failing/fails/.
> Typo: s/with error/with the error/.
> 
>> PROFILE_ERRIO neither a file stream is closed nor ctx is freed
>> in case of incorrect return status checking.
> 
> Strictly saying there are two problems:
> * Possible leakage for PROFILE_ERRRUN
> * Double free for PROFILE_ERRIO
> 
> So I propose the following wording:
> 
> | When memory profiler fails to start with PROFILE_ERRRUN status both
> | stream and ctx are not released. At the same time when memory profiler
> | fails to start with the PROFILE_ERRIO status both stream and ctx are
> | released twice. Both cases occur due to invalid return status checking.
> 
>> 
>> To avoid this behaviour on_stop callback is called manually inside
> 
> Minor: s/To avoid this behaviour/To fix the leakage/.
> 
>> the profiler when error on start is occurring. Checks in
> 
> Typo: s/is occuring/occurs/.
> 
>> misc.memprof.start() are omitted.
>> 
>> Follows up tarantool/tarantool#5442
>> ---
>> 
>> * How patch was checked:
>> Before patch you can occur the error like:
>> | $ src/luajit -e '
>> | local f, msg, errno = misc.memprof.start("/tmp/tmp_memprofile.bin")
>> | misc.memprof.start("/tmp/tmp_memprofile.bin") print(f,msg,errno)
>> | '
>> | true    nil     nil
>> | luajit: lj_state.c:178: close_state: Assertion `g->gc.total == sizeof(GG_State)' failed.
>> This patch fixes it.
>> 
>> * Why this assertion is not failed in tests (we have the test with same
>> functionality)?
>> This assertion failed inside close_state. Tarantool in some reason
>> doesn't call lua_close on stop. It's weird to me. I'll try to find an
>> explanation and will create a ticket.
>> 
>> * Why I don't create a test case.
>> The best idea is to do something like this and waiting for OOM:
>> | for _ = 1, 10000 do
>> |   misc.memprof.start("/tmp/tmp_memprofile.bin")
>> | end
>> But it's disgusting, so as I've discussed with Igor offline test case
>> will be ommited.
> 
> Side note: The test aims to hit LUA_ERRMEM and need to be run for a long
> time. The exact reason we didn't face this failure is the omitted
> <lua_close> in Tarantool.
> 
>> 
>> src/lib_misc.c   | 4 ----
>> src/lj_memprof.c | 8 ++++++--
>> 2 files changed, 6 insertions(+), 6 deletions(-)
>> 
> 
> <snipped>
> 
>> 
>> -- 
>> 2.28.0
>> 
> 
> -- 
> Best regards,
> IM


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