From: "Burakov, Anatoly" <anatoly.burakov@intel.com>
To: Andrew Rybchenko <arybchenko@solarflare.com>, dev@dpdk.org
Cc: bruce.richardson@intel.com, thomas@monjalon.net
Subject: Re: [dpdk-dev] [PATCH v3 2/2] mem: revert to using flock() and add per-segment lockfiles
Date: Mon, 30 Apr 2018 12:31:02 +0100 [thread overview]
Message-ID: <40b42df8-cc22-e529-e85c-c41edc36a0ff@intel.com> (raw)
In-Reply-To: <925daa23-9265-2547-720b-4048ba7aa623@solarflare.com>
On 28-Apr-18 10:38 AM, Andrew Rybchenko wrote:
> On 04/25/2018 01:36 PM, Anatoly Burakov wrote:
>> The original implementation used flock() locks, but was later
>> switched to using fcntl() locks for page locking, because
>> fcntl() locks allow locking parts of a file, which is useful
>> for single-file segments mode, where locking the entire file
>> isn't as useful because we still need to grow and shrink it.
>>
>> However, according to fcntl()'s Ubuntu manpage [1], semantics of
>> fcntl() locks have a giant oversight:
>>
>> This interface follows the completely stupid semantics of System
>> V and IEEE Std 1003.1-1988 (“POSIX.1”) that require that all
>> locks associated with a file for a given process are removed
>> when any file descriptor for that file is closed by that process.
>> This semantic means that applications must be aware of any files
>> that a subroutine library may access.
>>
>> Basically, closing *any* fd with an fcntl() lock (which we do because
>> we don't want to leak fd's) will drop the lock completely.
>>
>> So, in this commit, we will be reverting back to using flock() locks
>> everywhere. However, that still leaves the problem of locking parts
>> of a memseg list file in single file segments mode, and we will be
>> solving it with creating separate lock files per each page, and
>> tracking those with flock().
>>
>> We will also be removing all of this tailq business and replacing it
>> with a simple array - saving a few bytes is not worth the extra
>> hassle of dealing with pointers and potential memory allocation
>> failures. Also, remove the tailq lock since it is not needed - these
>> fd lists are per-process, and within a given process, it is always
>> only one thread handling access to hugetlbfs.
>>
>> So, first one to allocate a segment will create a lockfile, and put
>> a shared lock on it. When we're shrinking the page file, we will be
>> trying to take out a write lock on that lockfile, which would fail if
>> any other process is holding onto the lockfile as well. This way, we
>> can know if we can shrink the segment file. Also, if no other locks
>> are found in the lock list for a given memseg list, the memseg list
>> fd is automatically closed.
>>
>> One other thing to note is, according to flock() Ubuntu manpage [2],
>> upgrading the lock from shared to exclusive is implemented by dropping
>> and reacquiring the lock, which is not atomic and thus would have
>> created race conditions. So, on attempting to perform operations in
>> hugetlbfs, we will take out a writelock on hugetlbfs directory, so
>> that only one process could perform hugetlbfs operations concurrently.
>>
>> [1]
>> http://manpages.ubuntu.com/manpages/artful/en/man2/fcntl.2freebsd.html
>> [2] http://manpages.ubuntu.com/manpages/bionic/en/man2/flock.2.html
>>
>> Fixes: 66cc45e293ed ("mem: replace memseg with memseg lists")
>> Fixes: 582bed1e1d1d ("mem: support mapping hugepages at runtime")
>> Fixes: a5ff05d60fc5 ("mem: support unmapping pages at runtime")
>> Fixes: 2a04139f66b4 ("eal: add single file segments option")
>> Cc: anatoly.burakov@intel.com
>>
>> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
>> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
>
> We have a problem with the changeset if EAL option -m or --socket-mem is
> used.
> EAL initialization hangs just after EAL: Probing VFIO support...
> strace points to flock(7, LOCK_EX
> List of file descriptors:
> # ls /proc/25452/fd -l
> total 0
> lrwx------ 1 root root 64 Apr 28 10:34 0 -> /dev/pts/0
> lrwx------ 1 root root 64 Apr 28 10:34 1 -> /dev/pts/0
> lrwx------ 1 root root 64 Apr 28 10:32 2 -> /dev/pts/0
> lrwx------ 1 root root 64 Apr 28 10:34 3 -> /run/.rte_config
> lrwx------ 1 root root 64 Apr 28 10:34 4 -> socket:[154166]
> lrwx------ 1 root root 64 Apr 28 10:34 5 -> socket:[154158]
> lr-x------ 1 root root 64 Apr 28 10:34 6 -> /dev/hugepages
> lr-x------ 1 root root 64 Apr 28 10:34 7 -> /dev/hugepages
>
> I guess the problem is that there are two /dev/hugepages and
> it hangs on the second.
>
> Ideas how to solve it?
>
> Andrew.
>
Hi Andrew,
Please try the following patch:
http://dpdk.org/dev/patchwork/patch/39166/
This should fix the issue.
--
Thanks,
Anatoly
next prev parent reply other threads:[~2018-04-30 11:31 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-19 12:26 [dpdk-dev] [PATCH 0/2] Fix file locking in EAL memory Anatoly Burakov
2018-04-19 12:26 ` [dpdk-dev] [PATCH 1/2] mem: add memalloc init stage Anatoly Burakov
2018-04-24 14:06 ` Bruce Richardson
2018-04-19 12:26 ` [dpdk-dev] [PATCH 2/2] mem: revert to using flock() and add per-segment lockfiles Anatoly Burakov
2018-04-24 13:57 ` Bruce Richardson
2018-04-24 14:07 ` Bruce Richardson
2018-04-24 15:54 ` [dpdk-dev] [PATCH v2 0/2] Fix file locking in EAL memory Anatoly Burakov
2018-04-24 16:32 ` Stephen Hemminger
2018-04-24 17:25 ` Burakov, Anatoly
2018-04-24 20:05 ` Thomas Monjalon
2018-04-24 20:34 ` Stephen Hemminger
2018-04-25 10:36 ` [dpdk-dev] [PATCH v3 " Anatoly Burakov
2018-04-27 21:50 ` Thomas Monjalon
2018-04-25 10:36 ` [dpdk-dev] [PATCH v3 1/2] mem: add memalloc init stage Anatoly Burakov
2018-04-25 10:36 ` [dpdk-dev] [PATCH v3 2/2] mem: revert to using flock() and add per-segment lockfiles Anatoly Burakov
2018-04-28 9:38 ` Andrew Rybchenko
2018-04-30 8:29 ` Burakov, Anatoly
2018-04-30 11:31 ` Burakov, Anatoly [this message]
2018-04-30 11:51 ` Maxime Coquelin
2018-04-30 13:08 ` Andrew Rybchenko
2018-04-24 15:54 ` [dpdk-dev] [PATCH v2 1/2] mem: add memalloc init stage Anatoly Burakov
2018-04-24 15:54 ` [dpdk-dev] [PATCH v2 2/2] mem: revert to using flock() and add per-segment lockfiles Anatoly Burakov
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