From: Junio C Hamano <gitster@pobox.com>
To: Mathias Krause <minipli@grsecurity.net>
Cc: git@vger.kernel.org, "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"Carlo Marcelo Arenas Belón" <carenas@gmail.com>
Subject: Re: [PATCH v2] grep: fall back to interpreter if JIT memory allocation fails
Date: Fri, 27 Jan 2023 09:39:28 -0800 [thread overview]
Message-ID: <xmqq1qnfancf.fsf@gitster.g> (raw)
In-Reply-To: <xmqqbkmk9bsn.fsf@gitster.g> (Junio C. Hamano's message of "Fri, 27 Jan 2023 08:34:16 -0800")
Junio C Hamano <gitster@pobox.com> writes:
> Yes, the "instead of failing hard, fall back" makes sense. Just
> that I do not see why the runtime test is a good thing to have. In
> short, we are not in the business of catching bugs in pcre2_jit
> implementations, so if they say they cannot compile the pattern (I
> would even say I doubt the point of checking the return code to
> ensure it is NOMEMORY), it would be fine to let the interpreter
> codepath to inspect the pattern and diagnose problems with it, or
> take the slow match without JIT.
>
> What am I missing?
Note that I've seen and recently re-read the discussion that leads to
https://lore.kernel.org/git/f680b274-fa85-6624-096a-7753a2671c15@grsecurity.net/
I suspect that this auto-probe is related to solving "the user
thinks JIT is in use but because of failing JIT the user's pattern
is getting horrible performance" somehow. But I do not think a hard
failure is a good approach to help users in such a situation.
After such a failure, the user can prefix "(*NO_JIT)" to the pattern
and retry, or give up the operation altogether and not get a useful
result, but wouldn't it be far more helpful to just fallback as if
(*NO_JIT) was on from the beginning?
Also I notice that p->pcre2_jit_on is per "struct grep_pat", so it
is not like "once we see a pathological pattern, we turn off JIT
completely for other patterns", right? That is, if you have
git grep -P -e "$A" -e "$B"
and we fail to compile "$A" (for whatever reason), we could still
(attempt to) compile "$B". Perhaps $A was too complex or was
incompatible with JIT combined with other options, but $B may be
easy enough to still be JITtable, in which case we would match with
the JITted version of $B with interpreted version of $A, instead of
failing, right?
THanks.
next prev parent reply other threads:[~2023-01-27 17:39 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-16 12:15 [PATCH] grep: fall back to interpreter mode if JIT fails Mathias Krause
2022-12-16 16:12 ` Ævar Arnfjörð Bjarmason
2022-12-16 19:26 ` Mathias Krause
2022-12-16 23:09 ` Junio C Hamano
2022-12-17 2:50 ` Carlo Arenas
2022-12-19 9:00 ` Ævar Arnfjörð Bjarmason
2022-12-20 19:29 ` Mathias Krause
2022-12-20 21:11 ` Ævar Arnfjörð Bjarmason
2023-01-18 14:22 ` Mathias Krause
2023-01-18 15:44 ` Ævar Arnfjörð Bjarmason
2023-01-19 9:19 ` Mathias Krause
2022-12-16 22:52 ` Junio C Hamano
2022-12-20 20:40 ` Mathias Krause
2023-01-27 15:49 ` [PATCH v2] grep: fall back to interpreter if JIT memory allocation fails Mathias Krause
2023-01-27 16:34 ` Junio C Hamano
2023-01-27 17:39 ` Junio C Hamano [this message]
2023-01-27 18:46 ` Junio C Hamano
2023-01-29 13:37 ` Mathias Krause
2023-01-29 13:36 ` Mathias Krause
2023-01-29 17:15 ` Junio C Hamano
2023-01-30 10:56 ` Ævar Arnfjörð Bjarmason
2023-01-30 18:49 ` Junio C Hamano
2023-01-31 8:34 ` Ævar Arnfjörð Bjarmason
2023-01-30 11:08 ` Mathias Krause
2023-01-30 18:54 ` Junio C Hamano
2023-01-30 20:08 ` Junio C Hamano
2023-01-30 21:21 ` Junio C Hamano
2023-01-30 22:30 ` Ramsay Jones
2023-01-30 23:27 ` Junio C Hamano
2023-01-31 7:48 ` Mathias Krause
2023-01-31 16:41 ` Junio C Hamano
2023-01-31 18:34 ` Mathias Krause
2023-01-31 7:30 ` Mathias Krause
2023-01-29 12:28 ` Mathias Krause
2023-01-31 18:56 ` [PATCH v3] " Mathias Krause
2023-01-31 21:05 ` Junio C Hamano
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