From: Jamie Lokier <jamie@shareable.org> To: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Tejun Heo <tj@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Al Viro <viro@ZenIV.linux.org.uk>, Hugh Dickins <hugh@veritas.com>, Alexey Dobriyan <adobriyan@gmail.com>, Linus Torvalds <torvalds@linux-foundation.org>, Alan Cox <alan@lxorguk.ukuu.org.uk>, Greg Kroah-Hartman <gregkh@suse.de> Subject: Re: [RFC][PATCH 0/9] File descriptor hot-unplug support Date: Tue, 14 Apr 2009 16:07:45 +0100 [thread overview] Message-ID: <20090414150745.GC26621@shareable.org> (raw) In-Reply-To: <m18wm38ws1.fsf@fess.ebiederm.org> Eric W. Biederman wrote: > > I don't have anything at hand but multithread/process server accepting > > on the same socket comes to mind. I don't think it would be a very > > rare thing. If you confine the scope to character devices or sysfs, > > it could be quite rare tho. > > Yes. I think I can safely exclude sockets, and not bother with > reference counting them. Good idea. As well as many processes calling accept(), it's not unusual to have two threads or processes for reading and writing concurrently to TCP sockets, and to have a single UDP socket shared among threads/processes for sendto. > The only strong evidence I have that multi-threading on a single file > descriptor is likely to be common is that we have pread and pwrite > syscalls. At the same time the number of races we have in struct file > if it is accessed by multiple threads at the same time, suggests > that at least for cases where you have an offset it doesn't happen often. Notice the preadv and pwritev syscalls added recently? They were added because QEMU and KVM need them for performance. Those programs have multiple threads doing I/O to the same file concurrently. It's like a poor man's AIO, except it's more reliable than real Linux AIO :-) Databases probably should use concurrent p{read,write}{,v} if they're not using direct I/O and AIO. I'm not sure if the well-known databases do. In the past there have been some poor quality "emulations" of those syscalls prone to races, on Linux and BSD I believe. What are the races you've noticed? -- Jamie
WARNING: multiple messages have this Message-ID (diff)
From: Jamie Lokier <jamie@shareable.org> To: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Tejun Heo <tj@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Al Viro <viro@ZenIV.linux.org.uk>, Hugh Dickins <hugh@veritas.com>, Alexey Dobriyan <adobriyan@gmail.com>, Linus Torvalds <torvalds@linux-foundation.org>, Alan Cox <alan@lxorguk.ukuu.org.uk>, Greg Kroah-Hartman <gregkh@suse.de> Subject: Re: [RFC][PATCH 0/9] File descriptor hot-unplug support Date: Tue, 14 Apr 2009 16:07:45 +0100 [thread overview] Message-ID: <20090414150745.GC26621@shareable.org> (raw) In-Reply-To: <m18wm38ws1.fsf@fess.ebiederm.org> Eric W. Biederman wrote: > > I don't have anything at hand but multithread/process server accepting > > on the same socket comes to mind. I don't think it would be a very > > rare thing. If you confine the scope to character devices or sysfs, > > it could be quite rare tho. > > Yes. I think I can safely exclude sockets, and not bother with > reference counting them. Good idea. As well as many processes calling accept(), it's not unusual to have two threads or processes for reading and writing concurrently to TCP sockets, and to have a single UDP socket shared among threads/processes for sendto. > The only strong evidence I have that multi-threading on a single file > descriptor is likely to be common is that we have pread and pwrite > syscalls. At the same time the number of races we have in struct file > if it is accessed by multiple threads at the same time, suggests > that at least for cases where you have an offset it doesn't happen often. Notice the preadv and pwritev syscalls added recently? They were added because QEMU and KVM need them for performance. Those programs have multiple threads doing I/O to the same file concurrently. It's like a poor man's AIO, except it's more reliable than real Linux AIO :-) Databases probably should use concurrent p{read,write}{,v} if they're not using direct I/O and AIO. I'm not sure if the well-known databases do. In the past there have been some poor quality "emulations" of those syscalls prone to races, on Linux and BSD I believe. What are the races you've noticed? -- Jamie -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2009-04-14 15:08 UTC|newest] Thread overview: 207+ messages / expand[flat|nested] mbox.gz Atom feed top 2009-04-11 12:01 [RFC][PATCH 0/9] File descriptor hot-unplug support Eric W. Biederman 2009-04-11 12:01 ` Eric W. Biederman 2009-04-11 12:03 ` [RFC][PATCH 1/9] mm: Introduce remap_file_mappings Eric W. Biederman 2009-04-11 12:03 ` Eric W. Biederman 2009-04-11 12:05 ` [RFC][PATCH 2/9] mm: Implement generic support for revoking a mapping Eric W. Biederman 2009-04-11 12:05 ` Eric W. Biederman 2009-04-11 12:05 ` Eric W. Biederman 2009-04-11 12:06 ` [RFC][PATCH 3/9] sysfs: Use remap_file_mappings Eric W. Biederman 2009-04-11 12:06 ` Eric W. Biederman 2009-04-11 12:06 ` Eric W. Biederman 2009-04-11 12:07 ` [RFC][PATCH 4/9] vfs: Generalize the file_list Eric W. Biederman 2009-04-11 12:07 ` Eric W. Biederman 2009-04-11 12:07 ` Eric W. Biederman 2009-04-11 12:08 ` [RFC][PATCH 5/9] vfs: Introduce basic infrastructure for revoking a file Eric W. Biederman 2009-04-11 12:08 ` Eric W. Biederman 2009-04-11 12:08 ` Eric W. Biederman 2009-04-14 22:12 ` Jonathan Corbet 2009-04-14 22:12 ` Jonathan Corbet 2009-04-15 2:55 ` Eric W. Biederman 2009-04-15 2:55 ` Eric W. Biederman 2009-04-15 2:55 ` Eric W. Biederman 2009-04-11 12:10 ` [RFC][PATCH 6/9] vfs: Utilize fops_read_lock where appropriate Eric W. Biederman 2009-04-11 12:10 ` Eric W. Biederman 2009-04-11 12:10 ` Eric W. Biederman 2009-04-11 12:11 ` [RFC][PATCH 7/9] vfs: Optimize fops_read_lock Eric W. Biederman 2009-04-11 12:11 ` Eric W. Biederman 2009-04-11 12:11 ` Eric W. Biederman 2009-04-11 12:13 ` [RFC][PATCH 8/9] vfs: Implement generic revoked file operations Eric W. Biederman 2009-04-11 12:13 ` Eric W. Biederman 2009-04-11 12:13 ` Eric W. Biederman 2009-04-12 18:56 ` Jamie Lokier 2009-04-12 18:56 ` Jamie Lokier 2009-04-12 20:04 ` Eric W. Biederman 2009-04-12 20:04 ` Eric W. Biederman 2009-04-12 20:31 ` Jamie Lokier 2009-04-12 20:31 ` Jamie Lokier 2009-04-12 21:53 ` Eric W. Biederman 2009-04-12 21:53 ` Eric W. Biederman 2009-04-12 20:54 ` Eric W. Biederman 2009-04-12 20:54 ` Eric W. Biederman 2009-04-12 21:02 ` Jamie Lokier 2009-04-12 21:02 ` Jamie Lokier 2009-04-12 23:06 ` Eric W. Biederman 2009-04-12 23:06 ` Eric W. Biederman 2009-04-11 12:14 ` [RFC][PATCH 9/9] proc: Use the generic vfs revoke facility that now exists Eric W. Biederman 2009-04-11 12:14 ` Eric W. Biederman 2009-04-11 15:58 ` [RFC][PATCH 0/9] File descriptor hot-unplug support Al Viro 2009-04-11 15:58 ` Al Viro 2009-04-11 16:49 ` Eric W. Biederman 2009-04-11 16:49 ` Eric W. Biederman 2009-04-11 16:56 ` Al Viro 2009-04-11 16:56 ` Al Viro 2009-04-11 23:57 ` Eric W. Biederman 2009-04-11 23:57 ` Eric W. Biederman 2009-04-12 20:21 ` Eric W. Biederman 2009-04-12 20:21 ` Eric W. Biederman 2009-04-14 3:16 ` Tejun Heo 2009-04-14 3:16 ` Tejun Heo 2009-04-14 7:39 ` Eric W. Biederman 2009-04-14 7:39 ` Eric W. Biederman 2009-04-14 7:45 ` Tejun Heo 2009-04-14 7:45 ` Tejun Heo 2009-04-14 8:27 ` Eric W. Biederman 2009-04-14 8:27 ` Eric W. Biederman 2009-04-14 8:49 ` Tejun Heo 2009-04-14 8:49 ` Tejun Heo 2009-04-14 15:07 ` Jamie Lokier [this message] 2009-04-14 15:07 ` Jamie Lokier 2009-04-14 19:09 ` Eric W. Biederman 2009-04-14 19:09 ` Eric W. Biederman 2009-06-01 21:45 ` [PATCH 0/23] File descriptor hot-unplug support v2 Eric W. Biederman 2009-06-01 21:45 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 01/23] mm: Introduce revoke_file_mappings Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 22:25 ` Andrew Morton 2009-06-01 22:25 ` Andrew Morton 2009-06-02 0:12 ` Eric W. Biederman 2009-06-02 0:12 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 02/23] vfs: Implement unpoll_file Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-06 8:08 ` Al Viro 2009-06-06 8:08 ` Al Viro 2009-06-01 21:50 ` [PATCH 03/23] vfs: Generalize the file_list Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-02 7:06 ` Nick Piggin 2009-06-02 7:06 ` Nick Piggin 2009-06-05 19:33 ` Eric W. Biederman 2009-06-05 19:33 ` Eric W. Biederman 2009-06-09 10:38 ` Nick Piggin 2009-06-09 10:38 ` Nick Piggin 2009-06-09 18:38 ` Eric W. Biederman 2009-06-09 18:38 ` Eric W. Biederman 2009-06-10 6:05 ` Nick Piggin 2009-06-10 6:05 ` Nick Piggin 2009-06-01 21:50 ` [PATCH 04/23] vfs: Introduce infrastructure for revoking a file Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-02 5:16 ` Pekka Enberg 2009-06-02 5:16 ` Pekka Enberg 2009-06-02 6:51 ` Eric W. Biederman 2009-06-02 6:51 ` Eric W. Biederman 2009-06-02 7:08 ` Pekka Enberg 2009-06-02 7:08 ` Pekka Enberg 2009-06-02 7:08 ` Pekka Enberg 2009-06-02 7:14 ` Nick Piggin 2009-06-02 7:14 ` Nick Piggin 2009-06-02 17:06 ` Linus Torvalds 2009-06-02 17:06 ` Linus Torvalds 2009-06-02 20:52 ` Eric W. Biederman 2009-06-02 20:52 ` Eric W. Biederman 2009-06-03 6:37 ` Nick Piggin 2009-06-03 6:37 ` Nick Piggin 2009-06-02 22:56 ` Eric W. Biederman 2009-06-02 22:56 ` Eric W. Biederman 2009-06-03 6:38 ` Nick Piggin 2009-06-03 6:38 ` Nick Piggin 2009-06-05 9:03 ` Miklos Szeredi 2009-06-05 9:03 ` Miklos Szeredi 2009-06-05 19:06 ` Eric W. Biederman 2009-06-05 19:06 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 05/23] vfs: Teach lseek to use file_hotplug_lock Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 06/23] vfs: Teach read/write to use file_hotplug_read_lock Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 07/23] vfs: Teach sendfile,splice,tee,and vmsplice to use file_hotplug_lock Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-03 23:39 ` Badari Pulavarty 2009-06-03 23:39 ` Badari Pulavarty 2009-06-05 19:37 ` Eric W. Biederman 2009-06-05 19:37 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 08/23] vfs: Teach readdir " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 09/23] vfs: Teach poll and select " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 10/23] vfs: Teach do_path_lookup " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 11/23] mm: Teach mmap " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 12/23] vfs: Teach fcntl " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 13/23] vfs: Teach ioctl " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 14/23] vfs: Teach flock " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 15/23] vfs: Teach fallocate, and filp_close " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 16/23] vfs: Teach fstatfs, fstatfs64, ftruncate, fchdir, fchmod, fchown " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 17/23] proc: Teach /proc/<pid>/fd " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 18/23] vfs: Teach epoll " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-02 16:51 ` Davide Libenzi 2009-06-02 16:51 ` Davide Libenzi 2009-06-02 21:23 ` Eric W. Biederman 2009-06-02 21:23 ` Eric W. Biederman 2009-06-02 21:52 ` Davide Libenzi 2009-06-02 21:52 ` Davide Libenzi 2009-06-02 22:51 ` Eric W. Biederman 2009-06-02 22:51 ` Eric W. Biederman 2009-06-03 14:57 ` Davide Libenzi 2009-06-03 14:57 ` Davide Libenzi 2009-06-03 20:53 ` Eric W. Biederman 2009-06-03 20:53 ` Eric W. Biederman 2009-06-04 0:50 ` Davide Libenzi 2009-06-04 0:50 ` Davide Libenzi 2009-06-04 1:42 ` Eric W. Biederman 2009-06-04 1:42 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 19/23] eventpoll: Fix comment Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 20/23] vfs: Teach aio to use file_hotplug_lock Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 21/23] vfs: Teach fsync " Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 22/23] vfs: Teach fadvice to file_hotplug_lock Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-01 21:50 ` [PATCH 23/23] vfs: Teach readahead to use the file_hotplug_lock Eric W. Biederman 2009-06-01 21:50 ` Eric W. Biederman 2009-06-03 23:25 ` Badari Pulavarty 2009-06-03 23:25 ` Badari Pulavarty 2009-06-06 8:03 ` [PATCH 0/23] File descriptor hot-unplug support v2 Al Viro 2009-06-06 8:03 ` Al Viro 2009-06-08 9:41 ` Miklos Szeredi 2009-06-08 9:41 ` Miklos Szeredi 2009-06-08 10:24 ` Jamie Lokier 2009-06-08 10:24 ` Jamie Lokier 2009-06-08 16:29 ` Al Viro 2009-06-08 16:29 ` Al Viro 2009-06-08 16:44 ` Miklos Szeredi 2009-06-08 16:44 ` Miklos Szeredi 2009-06-08 17:50 ` Al Viro 2009-06-08 17:50 ` Al Viro 2009-06-08 18:01 ` Linus Torvalds 2009-06-08 18:01 ` Linus Torvalds 2009-06-08 18:50 ` Al Viro 2009-06-08 18:50 ` Al Viro 2009-06-08 19:18 ` Linus Torvalds 2009-06-08 19:18 ` Linus Torvalds 2009-06-09 6:42 ` Eric W. Biederman 2009-06-09 6:42 ` Eric W. Biederman 2009-06-09 10:52 ` Nick Piggin 2009-06-09 10:52 ` Nick Piggin 2009-06-09 5:50 ` Miklos Szeredi 2009-06-09 5:50 ` Miklos Szeredi 2009-06-09 6:31 ` Eric W. Biederman 2009-06-09 6:31 ` Eric W. Biederman 2009-06-09 6:22 ` Eric W. Biederman 2009-06-09 6:22 ` Eric W. Biederman
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