From: Siddhesh Poyarekar <siddhesh@sourceware.org>
To: Florian Weimer <fweimer@redhat.com>,
Siddhesh Poyarekar via Libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [PATCH] malloc: Ensure that ptmalloc_init runs only once
Date: Fri, 18 Jun 2021 08:01:30 +0530 [thread overview]
Message-ID: <68f4386f-9ae5-8791-31bf-7dcf14479847@sourceware.org> (raw)
In-Reply-To: <87a6no4l71.fsf@oldenburg.str.redhat.com>
On 6/17/21 8:01 PM, Florian Weimer via Libc-alpha wrote:
> * Siddhesh Poyarekar via Libc-alpha:
>
>> It is possible that multiple threads simultaneously enter
>> ptmalloc_init and succeed the < 0 check. Make the comparison and
>> setting of __malloc_initialized atomic so that only one of them goes
>> through. Additionally, if a thread sees that another thread is
>> running the initialization (i.e. __malloc_initialized == 0) then wait
>> till it is done.
>
> No, this cannot happen because pthread_create calls malloc before
> creating the new thread.
Yes but I wonder if we should rely on that. If we decide to rely on
this semantic then we implicitly specify thread creation through methods
other than pthread_create that happen to not call malloc as unsupported.
AFAICT it's not just a QOI issue; it may not be safe to call
malloc_init_state twice on the same arena through different threads.
Siddhesh
next prev parent reply other threads:[~2021-06-18 2:31 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-17 10:32 Siddhesh Poyarekar
2021-06-17 14:31 ` Florian Weimer
2021-06-18 2:31 ` Siddhesh Poyarekar [this message]
2021-06-18 5:45 ` Florian Weimer
2021-06-18 5:51 ` Siddhesh Poyarekar
2021-06-18 5:55 ` Florian Weimer
2021-06-18 6:28 ` Siddhesh Poyarekar
2021-06-18 6:32 ` Siddhesh Poyarekar
2021-06-18 6:36 ` Florian Weimer
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