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Date: Fri, 29 Feb 2008 21:52:24 +0100
From: Jens Axboe <jens.axboe@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Allard Hoeve <allard@...e.nl>, linux-kernel@...r.kernel.org,
Neil Brown <neilb@...e.de>
Subject: Re: Scheduler lockup or nfsd problem in 2.6.24.2 and 2.6.23.17?
On Thu, Feb 28 2008, Andrew Morton wrote:
> On Thu, 28 Feb 2008 15:04:12 +0100 (CET) Allard Hoeve <allard@...e.nl> wrote:
>
> >
> > Hello all,
> >
> > The last few days our trusty NFS server has experienced several soft
> > lockups. These occur every 11 hours or so. The system does not respond
> > afterwards. Sending sysrq commands over the serial console seems to work
> > allthough we had to powercycle the server once.
> >
> > First we thought it would be an NFS problem, and now that we tried
> > 2.6.23.17 instead of 2.6.24.2, we now have two different stacktraces that
> > share a trace through nfsd (nfsd_direct_splice_actor):
> >
> > http://article.gmane.org/gmane.linux.nfs/19107
>
> This:
>
> BUG: soft lockup - CPU#0 stuck for 11s! [nfsd:2716]
>
> Pid: 2716, comm: nfsd Not tainted (2.6.24.2-fwsh-byte #2)
> EIP: 0060:[<c0140967>] EFLAGS: 00000286 CPU: 0
> EIP is at find_get_pages_contig+0x67/0x73
> EAX: 00000000 EBX: 00000001 ECX: c25cc520 EDX: c25cc520
> ESI: 00000078 EDI: ca2fbdbc EBP: 00000001 ESP: dffb5c6c
> DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
> CR0: 8005003b CR2: b7f5d000 CR3: 1fc45000 CR4: 000006f0
> DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
> DR6: ffff0ff0 DR7: 00000400
> [<c017c49c>] __generic_file_splice_read+0xa2/0x41e
> [<c0113b11>] sched_slice+0x15/0x6f
> [<c0131291>] getnstimeofday+0x31/0x105
> [<c0134301>] clockevents_program_event+0xbf/0x134
> [<c012ef49>] ktime_get_ts+0x15/0x47
> [<c01231ea>] run_timer_softirq+0x30/0x184
> [<c012a893>] __rcu_process_callbacks+0x76/0xbb
> [<c011f979>] tasklet_action+0x53/0x93
> [<c011f754>] __do_softirq+0xba/0xcf
> [<c010e20e>] smp_apic_timer_interrupt+0x2c/0x35
> [<c01032e0>] apic_timer_interrupt+0x28/0x30
> [<c017c88d>] generic_file_splice_read+0x75/0xc9
> [<c017d083>] do_splice_to+0x6e/0x90
> [<c017d144>] splice_direct_to_actor+0x9f/0x166
> [<f8f2cf72>] nfsd_direct_splice_actor+0x0/0xa [nfsd]
> [<c017c818>] generic_file_splice_read+0x0/0xc9
> [<f8f2d309>] nfsd_vfs_read+0x38d/0x3b1 [nfsd]
> [<f8f2b3b8>] nfsd_acceptable+0x0/0xd1 [nfsd]
> [<c016014f>] dentry_open+0x34/0x64
> [<f8f2d73c>] nfsd_read+0xee/0xfb [nfsd]
> [<f8f33b8b>] nfsd3_proc_read+0xfe/0x186 [nfsd]
> [<f8f354cb>] nfs3svc_decode_readargs+0x0/0xeb [nfsd]
> [<f8f29855>] nfsd_dispatch+0xc5/0x1ac [nfsd]
> [<c0445ab2>] svcauth_unix_set_client+0x116/0x165
> [<c0441ad1>] svc_process+0x4e9/0x6b4
> [<c01168e2>] default_wake_function+0x0/0x8
> [<f8f2963d>] nfsd+0x16a/0x290 [nfsd]
> [<f8f294d3>] nfsd+0x0/0x290 [nfsd]
> [<c0103463>] kernel_thread_helper+0x7/0x10
> =======================
>
> > http://article.gmane.org/gmane.linux.nfs/19130
> >
> > The second however, leads me to think the (relatively new) scheduler might
> > be involved through __check_preempt_curr_fair.
>
> Nope, it looks like the splice code got stuck
>
> > I'm now trying 2.6.22.19, which has a recent lockd issue with NFS fixed
> > but hasn't had the scheduler update.
> >
> > How do I go about debugging this problem? What do you experts think?
>
> This ex-expert has real worries about generic_file_splice_read(). For
> starters, if __generic_file_splice_read() decides to return zero all the
> time, that function will lock up.
>
> Anyway. Jens, I think we have a splice problem here.
I agree, that loop has been a point of contention before. So this is how
I would fix it - never repeat a __generic_file_splice_read(), just pass
back the short splice. And make __generic_file_splice_read() pass back
-EAGAIN correctly. diffstat is good, too :-)
Does this work?
diff --git a/fs/splice.c b/fs/splice.c
index 9b559ee..0254ec6 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -370,8 +370,10 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
* for an in-flight io page
*/
if (flags & SPLICE_F_NONBLOCK) {
- if (TestSetPageLocked(page))
+ if (TestSetPageLocked(page)) {
+ error = -EAGAIN;
break;
+ }
} else
lock_page(page);
@@ -479,9 +481,8 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
struct pipe_inode_info *pipe, size_t len,
unsigned int flags)
{
- ssize_t spliced;
- int ret;
loff_t isize, left;
+ int ret;
isize = i_size_read(in->f_mapping->host);
if (unlikely(*ppos >= isize))
@@ -491,29 +492,9 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
if (unlikely(left < len))
len = left;
- ret = 0;
- spliced = 0;
- while (len && !spliced) {
- ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
-
- if (ret < 0)
- break;
- else if (!ret) {
- if (spliced)
- break;
- if (flags & SPLICE_F_NONBLOCK) {
- ret = -EAGAIN;
- break;
- }
- }
-
+ ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
+ if (ret > 0)
*ppos += ret;
- len -= ret;
- spliced += ret;
- }
-
- if (spliced)
- return spliced;
return ret;
}
--
Jens Axboe
--
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