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Message-ID: <5A4372AA.1080007@huawei.com> Date: Wed, 27 Dec 2017 18:15:06 +0800 From: piaojun <piaojun@...wei.com> To: Gang He <ghe@...e.com>, <mfasheh@...sity.com>, <jlbec@...lplan.org> CC: <linux-kernel@...r.kernel.org>, <ocfs2-devel@....oracle.com> Subject: Re: [Ocfs2-devel] [PATCH] ocfs2: try a blocking lock before return AOP_TRUNCATED_PAGE Hi Gang, Do you mean that too many retrys in loop cast losts of CPU-time and block page-fault interrupt? We should not add any delay in ocfs2_fault(), right? And I still feel a little confused why your method can solve this problem. thanks, Jun On 2017/12/27 17:29, Gang He wrote: > If we can't get inode lock immediately in the function > ocfs2_inode_lock_with_page() when reading a page, we should not > return directly here, since this will lead to a softlockup problem. > The method is to get a blocking lock and immediately unlock before > returning, this can avoid CPU resource waste due to lots of retries, > and benefits fairness in getting lock among multiple nodes, increase > efficiency in case modifying the same file frequently from multiple > nodes. > The softlockup problem looks like, > Kernel panic - not syncing: softlockup: hung tasks > CPU: 0 PID: 885 Comm: multi_mmap Tainted: G L 4.12.14-6.1-default #1 > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > Call Trace: > <IRQ> > dump_stack+0x5c/0x82 > panic+0xd5/0x21e > watchdog_timer_fn+0x208/0x210 > ? watchdog_park_threads+0x70/0x70 > __hrtimer_run_queues+0xcc/0x200 > hrtimer_interrupt+0xa6/0x1f0 > smp_apic_timer_interrupt+0x34/0x50 > apic_timer_interrupt+0x96/0xa0 > </IRQ> > RIP: 0010:unlock_page+0x17/0x30 > RSP: 0000:ffffaf154080bc88 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff10 > RAX: dead000000000100 RBX: fffff21e009f5300 RCX: 0000000000000004 > RDX: dead0000000000ff RSI: 0000000000000202 RDI: fffff21e009f5300 > RBP: 0000000000000000 R08: 0000000000000000 R09: ffffaf154080bb00 > R10: ffffaf154080bc30 R11: 0000000000000040 R12: ffff993749a39518 > R13: 0000000000000000 R14: fffff21e009f5300 R15: fffff21e009f5300 > ocfs2_inode_lock_with_page+0x25/0x30 [ocfs2] > ocfs2_readpage+0x41/0x2d0 [ocfs2] > ? pagecache_get_page+0x30/0x200 > filemap_fault+0x12b/0x5c0 > ? recalc_sigpending+0x17/0x50 > ? __set_task_blocked+0x28/0x70 > ? __set_current_blocked+0x3d/0x60 > ocfs2_fault+0x29/0xb0 [ocfs2] > __do_fault+0x1a/0xa0 > __handle_mm_fault+0xbe8/0x1090 > handle_mm_fault+0xaa/0x1f0 > __do_page_fault+0x235/0x4b0 > trace_do_page_fault+0x3c/0x110 > async_page_fault+0x28/0x30 > RIP: 0033:0x7fa75ded638e > RSP: 002b:00007ffd6657db18 EFLAGS: 00010287 > RAX: 000055c7662fb700 RBX: 0000000000000001 RCX: 000055c7662fb700 > RDX: 0000000000001770 RSI: 00007fa75e909000 RDI: 000055c7662fb700 > RBP: 0000000000000003 R08: 000000000000000e R09: 0000000000000000 > R10: 0000000000000483 R11: 00007fa75ded61b0 R12: 00007fa75e90a770 > R13: 000000000000000e R14: 0000000000001770 R15: 0000000000000000 > > Fixes: 1cce4df04f37 ("ocfs2: do not lock/unlock() inode DLM lock") > Signed-off-by: Gang He <ghe@...e.com> > --- > fs/ocfs2/dlmglue.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c > index 4689940..5193218 100644 > --- a/fs/ocfs2/dlmglue.c > +++ b/fs/ocfs2/dlmglue.c > @@ -2486,6 +2486,15 @@ int ocfs2_inode_lock_with_page(struct inode *inode, > ret = ocfs2_inode_lock_full(inode, ret_bh, ex, OCFS2_LOCK_NONBLOCK); > if (ret == -EAGAIN) { > unlock_page(page); > + /* > + * If we can't get inode lock immediately, we should not return > + * directly here, since this will lead to a softlockup problem. > + * The method is to get a blocking lock and immediately unlock > + * before returning, this can avoid CPU resource waste due to > + * lots of retries, and benefits fairness in getting lock. > + */ > + if (ocfs2_inode_lock(inode, ret_bh, ex) == 0) > + ocfs2_inode_unlock(inode, ex); > ret = AOP_TRUNCATED_PAGE; > } > >
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