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From: Rich Felker <dalias@libc.org>
To: Rabbitstack <rabbitstack7@gmail.com>
Cc: musl@lists.openwall.com
Subject: Re: setrlimit hangs the process
Date: Tue, 25 Sep 2018 11:13:36 -0400	[thread overview]
Message-ID: <20180925151336.GK17995@brightrain.aerifal.cx> (raw)
In-Reply-To: <CAA3hR4edEx3t+=gw2EYe3w2x2UJa6VwnhxcDn5y_Fuf3U+u0Zw@mail.gmail.com>

On Tue, Sep 25, 2018 at 04:54:37PM +0200, Rabbitstack wrote:
> Sorry. Let me describe the problem in more detail.
> 
> The process only hangs when launched without root privileges on the host
> (Arch Linux x64 with kernel 4.17.5-1) where Alpine docker container is
> running. Once with root privileges, it starts up correctly (but this is
> obvious since it doesn't hit setrlimit call). The odd side is that on other
> hosts it hangs even when started with root. No error messages so far.
> Strace output:
> 
> $ sudo strace -p 9285
> 
> futex(0x2cddfc0, FUTEX_WAIT_PRIVATE, 0, NULL
> 
> $ sudo strace -f -p 9285
> 
> ......
> [pid  9287] getdents64(10, /* 14 entries */, 2048) = 336
> [pid  9287] tgkill(9285, 9285, SIGRT_2) = 0
> [pid  9287] futex(0x7efbff70008c, FUTEX_LOCK_PI_PRIVATE,
> {tv_sec=1537887068, tv_nsec=51442144}) = -1 ETIMEDOUT (Connection timed out)
> [pid  9287] getdents64(10, /* 0 entries */, 2048) = 0
> [pid  9287] lseek(10, 0, SEEK_SET)      = 0
> [pid  9287] getdents64(10, /* 14 entries */, 2048) = 336
> [pid  9287] tgkill(9285, 9285, SIGRT_2) = 0
> [pid  9287] futex(0x7efbff70008c, FUTEX_LOCK_PI_PRIVATE,
> {tv_sec=1537887068, tv_nsec=62384239}) = -1 ETIMEDOUT (Connection timed out)
> [pid  9287] getdents64(10, /* 0 entries */, 2048) = 0
> [pid  9287] lseek(10, 0, SEEK_SET)      = 0
> [pid  9287] getdents64(10, /* 14 entries */, 2048) = 336
> [pid  9287] tgkill(9285, 9285, SIGRT_2) = 0
> [pid  9287] futex(0x7efbff70008c, FUTEX_LOCK_PI_PRIVATE,
> {tv_sec=1537887068, tv_nsec=73251219}) = -1 ETIMEDOUT (Connection timed out)
> [pid  9287] getdents64(10, /* 0 entries */, 2048) = 0
> [pid  9287] lseek(10, 0, SEEK_SET)      = 0
> [pid  9287] getdents64(10, /* 14 entries */, 2048) = 336
> [pid  9287] tgkill(9285, 9285, SIGRT_2) = 0
> [pid  9287] futex(0x7efbff70008c, FUTEX_LOCK_PI_PRIVATE,
> {tv_sec=1537887068, tv_nsec=84458579}) = -1 ETIMEDOUT (Connection timed out)
> [pid  9287] getdents64(10, /* 0 entries */, 2048) = 0
> [pid  9287] lseek(10, 0, SEEK_SET)      = 0
> [pid  9287] getdents64(10, /* 14 entries */, 2048) = 336
> [pid  9287] tgkill(9285, 9285, SIGRT_2) = 0
> [pid  9287] futex(0x7efbff70008c, FUTEX_LOCK_PI_PRIVATE,
> {tv_sec=1537887068, tv_nsec=95098614}) = -1 ETIMEDOUT (Connection timed out)
> [pid  9287] getdents64(10, /* 0 entries */, 2048) = 0
> [pid  9287] lseek(10, 0, SEEK_SET)      = 0
> [pid  9287] getdents64(10, /* 14 entries */, 2048) = 336
> [pid  9287] tgkill(9285, 9285, SIGRT_2) = 0
> [pid  9287] futex(0x7efbff70008c, FUTEX_LOCK_PI_PRIVATE,
> {tv_sec=1537887068, tv_nsec=106005502}) = -1 ETIMEDOUT (Connection timed
> out)
> [pid  9287] getdents64(10, /* 0 entries */, 2048) = 0
> [pid  9287] lseek(10, 0, SEEK_SET)      = 0
> [pid  9287] getdents64(10, /* 14 entries */, 2048) = 336
> [pid  9287] tgkill(9285, 9285, SIGRT_2) = 0
> ......
> 
> 
> I'll try to build a tiny example to isolate the problem and hopefully
> provide more feedback.

The trace here shows a thread, tid 9285, the main thread, not
responding to the broadcast signals that are necessary to stop all
threads for the purpose of changing resource limits, uids/gids/etc.
I'm guessing some part of the Go runtime has bypassed libc and blocked
libc-internal signals in the main thread. A full strace rather than a
truncated one like the above would show this happening. If you can
produce one that doesn't expose private data that would be helpful; if
not, perhaps it's possible to write a minimal Go program that
reproduces the issue and strace it instead.

Rich


  reply	other threads:[~2018-09-25 15:13 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-25 12:59 Rabbitstack
2018-09-25 14:15 ` Szabolcs Nagy
2018-09-25 14:54   ` Rabbitstack
2018-09-25 15:13     ` Rich Felker [this message]
2018-09-25 15:38       ` Szabolcs Nagy
2018-09-25 15:36     ` Szabolcs Nagy
2018-09-25 16:38       ` Rich Felker
2018-10-04 14:54         ` Rabbitstack
2018-10-04 15:04           ` Rich Felker
2018-10-04 15:41             ` Rabbitstack
2018-10-04 15:53               ` Rich Felker
2018-10-04 16:05                 ` Rabbitstack
2018-10-05  0:47                 ` Rich Felker
2018-10-09 19:37                   ` Rabbitstack
2018-10-09 19:45                     ` Rich Felker
2018-10-09 20:36                     ` Szabolcs Nagy
2018-10-09 20:40                       ` Rich Felker
2018-10-11 15:14                         ` Rabbitstack

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