Re: epoll_wait returning EFAULT on Linux 3.2.78

From: Andres Freund <andres(at)anarazel(dot)de>
To: Greg Stark <stark(at)mit(dot)edu>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: epoll_wait returning EFAULT on Linux 3.2.78
Date: 2016-06-02 17:04:34
Message-ID: 20160602170434.kn3qqcefrk7luaq3@alap3.anarazel.de
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Hi,

On 2016-06-02 17:50:20 +0100, Greg Stark wrote:
> So FYI, it does look like Postgres built in 32-bit mode, at least
> pointers are 32 bits. But I think maxalign might still be enough due
> to doubles being 64 bits.

That makes sense independent of 32 vs. 64 system. Part of the relevant
struct probably require 8 byte alignment:

typedef union epoll_data {
void *ptr;
int fd;
uint32_t u32;
uint64_t u64;
} epoll_data_t;

struct epoll_event {
uint32_t events; /* Epoll events */
epoll_data_t data; /* User data variable */
};

So using long long alignment seems the best bet here.

Greg, are you writing & testing a patch? Or should I write something for
you to test?

Regards,

Andres

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