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Date: Wed, 8 Dec 2010 14:28:13 +1100
From: Nick Piggin <npiggin@kernel.dk>
To: Nick Piggin <npiggin@gmail.com>
Cc: Dave Chinner <david@fromorbit.com>, Nick Piggin <npiggin@kernel.dk>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 00/46] rcu-walk and dcache scaling
Message-ID: <20101208032813.GA6812@amd>
References: <cover.1290852958.git.npiggin@kernel.dk>
 <20101207112555.GE16103@dastard>
 <AANLkTinAt9PEWMCP55o64E7wsfZ=depU+YXbG8DdGYdO@mail.gmail.com>
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On Wed, Dec 08, 2010 at 02:24:23AM +1100, Nick Piggin wrote:
> On Tue, Dec 7, 2010 at 10:25 PM, Dave Chinner <david@fromorbit.com> wrote:
> > [ 5954.061633] BUG: sleeping function called from invalid context at arch/x86/mm/fault.c:1081
> > [ 5954.062466] in_atomic(): 0, irqs_disabled(): 1, pid: 2927, name: rm
> > [ 5954.063122] 3 locks held by rm/2927:
> > [ 5954.063476]  #0:  (&sb->s_type->i_mutex_key#12/1){+.+.+.}, at: [<ffffffff8116f5e1>] do_rmdir+0x81/0x130
> > [ 5954.064014]  #1:  (&sb->s_type->i_mutex_key#12){+.+.+.}, at: [<ffffffff8116d3a8>] vfs_rmdir+0x58/0xe0
> > [ 5954.064014]  #2:  (rcu_read_lock){.+.+..}, at: [<ffffffff811779c0>] shrink_dentry_list+0x0/0x430
> > [ 5954.064014] irq event stamp: 1484376719
> > [ 5954.064014] hardirqs last  enabled at (1484376719): [<ffffffff810ebf07>] __call_rcu+0xd7/0x1a0
> > [ 5954.064014] hardirqs last disabled at (1484376718): [<ffffffff810ebe7a>] __call_rcu+0x4a/0x1a0
> > [ 5954.064014] softirqs last  enabled at (1484376586): [<ffffffff8108b911>] __do_softirq+0x161/0x270
> > [ 5954.064014] softirqs last disabled at (1484376581): [<ffffffff8103af1c>] call_softirq+0x1c/0x50
> > [ 5954.064014] Pid: 2927, comm: rm Not tainted 2.6.37-rc4-dgc+ #794
> > [ 5954.064014] Call Trace:
> > [ 5954.064014]  [<ffffffff810b95b0>] ? print_irqtrace_events+0xd0/0xe0
> > [ 5954.064014]  [<ffffffff81076455>] __might_sleep+0xf5/0x130
> > [ 5954.064014]  [<ffffffff81b1e603>] do_page_fault+0x103/0x4f0
> > [ 5954.064014]  [<ffffffff810645b8>] ? pvclock_clocksource_read+0x58/0xd0
> > [ 5954.064014]  [<ffffffff810645b8>] ? pvclock_clocksource_read+0x58/0xd0
> > [ 5954.064014]  [<ffffffff810645b8>] ? pvclock_clocksource_read+0x58/0xd0
> > [ 5954.064014]  [<ffffffff81b19b28>] ? trace_hardirqs_off_thunk+0x3a/0x3c
> > [ 5954.064014]  [<ffffffff810b8e20>] ? usage_match+0x0/0x20
> > [ 5954.064014]  [<ffffffff81b1af25>] page_fault+0x25/0x30
> > [ 5954.064014]  [<ffffffff810b8e20>] ? usage_match+0x0/0x20
> > [ 5954.064014]  [<ffffffff810ba1c8>] ? __bfs+0xc8/0x260
> > [ 5954.064014]  [<ffffffff810ba123>] ? __bfs+0x23/0x260
> > [ 5954.064014]  [<ffffffff810ba4d2>] find_usage_backwards+0x42/0x80
> > [ 5954.064014]  [<ffffffff810bcec4>] check_usage_backwards+0x64/0xf0
> > [ 5954.064014]  [<ffffffff8104796f>] ? save_stack_trace+0x2f/0x50
> > [ 5954.064014]  [<ffffffff810bce60>] ? check_usage_backwards+0x0/0xf0
> > [ 5954.064014]  [<ffffffff810bd9a9>] mark_lock+0x1a9/0x440
> > [ 5954.064014]  [<ffffffff810be989>] __lock_acquire+0x5a9/0x14b0
> > [ 5954.064014]  [<ffffffff810be716>] ? __lock_acquire+0x336/0x14b0
> > [ 5954.064014]  [<ffffffff810645b8>] ? pvclock_clocksource_read+0x58/0xd0
> > [ 5954.064014]  [<ffffffff810bf944>] lock_acquire+0xb4/0x140
> > [ 5954.064014]  [<ffffffff81177a1c>] ? shrink_dentry_list+0x5c/0x430
> > [ 5954.064014]  [<ffffffff81b19d86>] _raw_spin_lock+0x36/0x70
> > [ 5954.064014]  [<ffffffff81177a1c>] ? shrink_dentry_list+0x5c/0x430
> > [ 5954.064014]  [<ffffffff81177a1c>] shrink_dentry_list+0x5c/0x430
> > [ 5954.064014]  [<ffffffff811779c0>] ? shrink_dentry_list+0x0/0x430
> > [ 5954.064014]  [<ffffffff816b9c7e>] ? do_raw_spin_unlock+0x5e/0xb0
> > [ 5954.064014]  [<ffffffff81177f2d>] __shrink_dcache_sb+0x13d/0x1c0
> > [ 5954.064014]  [<ffffffff811784bf>] shrink_dcache_parent+0x32f/0x390
> > [ 5954.064014]  [<ffffffff8116d31d>] dentry_unhash+0x3d/0x70
> > [ 5954.064014]  [<ffffffff8116d3b0>] vfs_rmdir+0x60/0xe0
> > [ 5954.064014]  [<ffffffff8116f673>] do_rmdir+0x113/0x130
> > [ 5954.064014]  [<ffffffff8103a03a>] ? sysret_check+0x2e/0x69
> > [ 5954.064014]  [<ffffffff81b19ae9>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> > [ 5954.064014]  [<ffffffff8116f6c5>] sys_unlinkat+0x35/0x40
> > [ 5954.064014]  [<ffffffff8103a002>] system_call_fastpath+0x16/0x1b
> 
> Seems that lockdep exploded.
> 
> > [ 5954.092916] BUG: unable to handle kernel NULL pointer dereference at           (null)
> > [ 5954.093806] IP: [<ffffffff810ba1c8>] __bfs+0xc8/0x260
> > [ 5954.094331] PGD 1084e5067 PUD 102368067 PMD 0
> > [ 5954.094830] Oops: 0000 [#1] SMP
> > [ 5954.095194] last sysfs file: /sys/devices/system/cpu/online
> > [ 5954.095760] CPU 6
> > [ 5954.095954] Modules linked in:
> > [ 5954.096319]
> > [ 5954.096483] Pid: 2927, comm: rm Not tainted 2.6.37-rc4-dgc+ #794 /Bochs
> > [ 5954.096665] RIP: 0010:[<ffffffff810ba1c8>]  [<ffffffff810ba1c8>] __bfs+0xc8/0x260
> > [ 5954.096665] RSP: 0018:ffff8801175539a8  EFLAGS: 00010046
> > [ 5954.096665] RAX: ffffffff8267d980 RBX: ffffffff8267d980 RCX: ffff880117553a48
> > [ 5954.096665] RDX: ffff8801175539d0 RSI: 0000000000000000 RDI: ffff880117553a48
> > [ 5954.096665] RBP: ffff880117553a08 R08: 0000000000000000 R09: 0000000000000000
> > [ 5954.096665] R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
> > [ 5954.096665] R13: ffffffff810b8e20 R14: ffff880117553a90 R15: 0000000000000000
> > [ 5954.096665] FS:  00007f4594cf3700(0000) GS:ffff8800dfa00000(0000) knlGS:0000000000000000
> > [ 5954.096665] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > [ 5954.096665] CR2: 00007f2f21e89c60 CR3: 0000000110b0f000 CR4: 00000000000006e0
> > [ 5954.096665] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [ 5954.096665] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > [ 5954.096665] Process rm (pid: 2927, threadinfo ffff880117552000, task ffff88010ff10b00)
> > [ 5954.096665] Stack:
> > [ 5954.096665]  ffffffff8267d868 00007fffa02d1428 ffff8800ffffffff ffff880100000000
> > [ 5954.096665]  000000000000b720 ffff880117553a48 ffffffff8267d868 ffff880117553a48
> > [ 5954.096665]  0000000000000000 ffff88010ff10b00 0000000000000000 ffffffff81dacba0
> > [ 5954.096665] Call Trace:
> > [ 5954.096665]  [<ffffffff810ba4d2>] find_usage_backwards+0x42/0x80
> > [ 5954.096665]  [<ffffffff810bcec4>] check_usage_backwards+0x64/0xf0
> > [ 5954.096665]  [<ffffffff8104796f>] ? save_stack_trace+0x2f/0x50
> > [ 5954.096665]  [<ffffffff810bce60>] ? check_usage_backwards+0x0/0xf0
> > [ 5954.096665]  [<ffffffff810bd9a9>] mark_lock+0x1a9/0x440
> > [ 5954.096665]  [<ffffffff810be989>] __lock_acquire+0x5a9/0x14b0
> > [ 5954.096665]  [<ffffffff810be716>] ? __lock_acquire+0x336/0x14b0
> > [ 5954.096665]  [<ffffffff810645b8>] ? pvclock_clocksource_read+0x58/0xd0
> > [ 5954.096665]  [<ffffffff810bf944>] lock_acquire+0xb4/0x140
> > [ 5954.096665]  [<ffffffff81177a1c>] ? shrink_dentry_list+0x5c/0x430
> > [ 5954.096665]  [<ffffffff81b19d86>] _raw_spin_lock+0x36/0x70
> > [ 5954.096665]  [<ffffffff81177a1c>] ? shrink_dentry_list+0x5c/0x430
> > [ 5954.096665]  [<ffffffff81177a1c>] shrink_dentry_list+0x5c/0x430
> > [ 5954.096665]  [<ffffffff811779c0>] ? shrink_dentry_list+0x0/0x430
> > [ 5954.096665]  [<ffffffff816b9c7e>] ? do_raw_spin_unlock+0x5e/0xb0
> > [ 5954.096665]  [<ffffffff81177f2d>] __shrink_dcache_sb+0x13d/0x1c0
> > [ 5954.096665]  [<ffffffff811784bf>] shrink_dcache_parent+0x32f/0x390
> > [ 5954.096665]  [<ffffffff8116d31d>] dentry_unhash+0x3d/0x70
> > [ 5954.096665]  [<ffffffff8116d3b0>] vfs_rmdir+0x60/0xe0
> > [ 5954.096665]  [<ffffffff8116f673>] do_rmdir+0x113/0x130
> > [ 5954.096665]  [<ffffffff8103a03a>] ? sysret_check+0x2e/0x69
> > [ 5954.096665]  [<ffffffff81b19ae9>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> > [ 5954.096665]  [<ffffffff8116f6c5>] sys_unlinkat+0x35/0x40
> > [ 5954.096665]  [<ffffffff8103a002>] system_call_fastpath+0x16/0x1b
> > [ 5954.096665] Code: 0a 89 05 dc 0f a8 01 48 8b 41 10 48 85 c0 0f 84 1f 01 00 00 48 8d 98 70 01 00 00 48 05 80 01 00 00 45 85 c0 48 0f 44 d8 4c 8b 3b <49> 8b 07 49 39
> > [ 5954.096665] RIP  [<ffffffff810ba1c8>] __bfs+0xc8/0x260
> > [ 5954.096665]  RSP <ffff8801175539a8>
> > [ 5954.096665] CR2: 0000000000000000
> > [ 5954.127991] ---[ end trace 85a6727c2d4e3d90 ]---
> 
> So vfs-scale-working branch may not be entirely in the clear, seeing

Ah, may have been a stupid little bug. The list entry check was being done
and then the pointer reloaded to be used.

What does the asm for shrink_dentry_list look like (before this patch)?

Thanks,
Nick

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c	2010-12-08 12:41:35.000000000 +1100
+++ linux-2.6/fs/dcache.c	2010-12-08 14:23:46.000000000 +1100
@@ -657,10 +657,10 @@ static void shrink_dentry_list(struct li
 	struct dentry *dentry;
 
 	rcu_read_lock();
-	while (!list_empty(list)) {
-		dentry = list_entry(list->prev, struct dentry, d_lru);
-
-		/* Don't need RCU dereference because we recheck under lock */
+	for (;;) {
+		dentry = list_entry_rcu(list->prev, struct dentry, d_lru);
+		if (&dentry->d_lru == list)
+			break;
 		spin_lock(&dentry->d_lock);
 		if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
 			spin_unlock(&dentry->d_lock);