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Koen Kooi
189ce92b4c
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net> Signed-off-by: Denys Dmytriyenko <denys@ti.com>
131 lines
4.4 KiB
Diff
131 lines
4.4 KiB
Diff
From 72a350429f61098d46984c13e8da293ec7a8ffe4 Mon Sep 17 00:00:00 2001
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From: Miklos Szeredi <miklos@szeredi.hu>
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Date: Tue, 10 Jan 2012 18:22:25 +0100
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Subject: [PATCH 076/129] fix shrink_dcache_parent() livelock
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commit eaf5f9073533cde21c7121c136f1c3f072d9cf59 upstream.
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Two (or more) concurrent calls of shrink_dcache_parent() on the same dentry may
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cause shrink_dcache_parent() to loop forever.
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Here's what appears to happen:
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1 - CPU0: select_parent(P) finds C and puts it on dispose list, returns 1
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2 - CPU1: select_parent(P) locks P->d_lock
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3 - CPU0: shrink_dentry_list() locks C->d_lock
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dentry_kill(C) tries to lock P->d_lock but fails, unlocks C->d_lock
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4 - CPU1: select_parent(P) locks C->d_lock,
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moves C from dispose list being processed on CPU0 to the new
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dispose list, returns 1
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5 - CPU0: shrink_dentry_list() finds dispose list empty, returns
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6 - Goto 2 with CPU0 and CPU1 switched
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Basically select_parent() steals the dentry from shrink_dentry_list() and thinks
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it found a new one, causing shrink_dentry_list() to think it's making progress
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and loop over and over.
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One way to trigger this is to make udev calls stat() on the sysfs file while it
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is going away.
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Having a file in /lib/udev/rules.d/ with only this one rule seems to the trick:
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ATTR{vendor}=="0x8086", ATTR{device}=="0x10ca", ENV{PCI_SLOT_NAME}="%k", ENV{MATCHADDR}="$attr{address}", RUN+="/bin/true"
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Then execute the following loop:
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while true; do
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echo -bond0 > /sys/class/net/bonding_masters
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echo +bond0 > /sys/class/net/bonding_masters
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echo -bond1 > /sys/class/net/bonding_masters
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echo +bond1 > /sys/class/net/bonding_masters
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done
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One fix would be to check all callers and prevent concurrent calls to
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shrink_dcache_parent(). But I think a better solution is to stop the
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stealing behavior.
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This patch adds a new dentry flag that is set when the dentry is added to the
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dispose list. The flag is cleared in dentry_lru_del() in case the dentry gets a
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new reference just before being pruned.
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If the dentry has this flag, select_parent() will skip it and let
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shrink_dentry_list() retry pruning it. With select_parent() skipping those
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dentries there will not be the appearance of progress (new dentries found) when
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there is none, hence shrink_dcache_parent() will not loop forever.
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Set the flag is also set in prune_dcache_sb() for consistency as suggested by
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Linus.
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Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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---
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fs/dcache.c | 15 +++++++++++----
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include/linux/dcache.h | 1 +
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2 files changed, 12 insertions(+), 4 deletions(-)
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diff --git a/fs/dcache.c b/fs/dcache.c
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index 108116e..f7908ae 100644
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--- a/fs/dcache.c
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+++ b/fs/dcache.c
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@@ -242,6 +242,7 @@ static void dentry_lru_add(struct dentry *dentry)
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static void __dentry_lru_del(struct dentry *dentry)
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{
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list_del_init(&dentry->d_lru);
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+ dentry->d_flags &= ~DCACHE_SHRINK_LIST;
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dentry->d_sb->s_nr_dentry_unused--;
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dentry_stat.nr_unused--;
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}
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@@ -805,6 +806,7 @@ relock:
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spin_unlock(&dentry->d_lock);
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} else {
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list_move_tail(&dentry->d_lru, &tmp);
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+ dentry->d_flags |= DCACHE_SHRINK_LIST;
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spin_unlock(&dentry->d_lock);
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if (!--count)
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break;
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@@ -1096,14 +1098,19 @@ resume:
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/*
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* move only zero ref count dentries to the dispose list.
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+ *
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+ * Those which are presently on the shrink list, being processed
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+ * by shrink_dentry_list(), shouldn't be moved. Otherwise the
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+ * loop in shrink_dcache_parent() might not make any progress
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+ * and loop forever.
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*/
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- if (!dentry->d_count) {
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+ if (dentry->d_count) {
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+ dentry_lru_del(dentry);
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+ } else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) {
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dentry_lru_move_list(dentry, dispose);
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+ dentry->d_flags |= DCACHE_SHRINK_LIST;
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found++;
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- } else {
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- dentry_lru_del(dentry);
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}
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-
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/*
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* We can return to the caller if we have found some (this
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* ensures forward progress). We'll be coming back to find
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diff --git a/include/linux/dcache.h b/include/linux/dcache.h
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index ed9f74f..4eb8c80 100644
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--- a/include/linux/dcache.h
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+++ b/include/linux/dcache.h
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@@ -203,6 +203,7 @@ struct dentry_operations {
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#define DCACHE_CANT_MOUNT 0x0100
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#define DCACHE_GENOCIDE 0x0200
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+#define DCACHE_SHRINK_LIST 0x0400
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#define DCACHE_NFSFS_RENAMED 0x1000
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/* this dentry has been "silly renamed" and has to be deleted on the last
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--
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1.7.9.5
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