fix shrink_dcache_parent() livelock
Two (or more) concurrent calls of shrink_dcache_parent() on the same dentry may cause shrink_dcache_parent() to loop forever. Here's what appears to happen: 1 - CPU0: select_parent(P) finds C and puts it on dispose list, returns 1 2 - CPU1: select_parent(P) locks P->d_lock 3 - CPU0: shrink_dentry_list() locks C->d_lock dentry_kill(C) tries to lock P->d_lock but fails, unlocks C->d_lock 4 - CPU1: select_parent(P) locks C->d_lock, moves C from dispose list being processed on CPU0 to the new dispose list, returns 1 5 - CPU0: shrink_dentry_list() finds dispose list empty, returns 6 - Goto 2 with CPU0 and CPU1 switched Basically select_parent() steals the dentry from shrink_dentry_list() and thinks it found a new one, causing shrink_dentry_list() to think it's making progress and loop over and over. One way to trigger this is to make udev calls stat() on the sysfs file while it is going away. Having a file in /lib/udev/rules.d/ with only this one rule seems to the trick: ATTR{vendor}=="0x8086", ATTR{device}=="0x10ca", ENV{PCI_SLOT_NAME}="%k", ENV{MATCHADDR}="$attr{address}", RUN+="/bin/true" Then execute the following loop: while true; do echo -bond0 > /sys/class/net/bonding_masters echo +bond0 > /sys/class/net/bonding_masters echo -bond1 > /sys/class/net/bonding_masters echo +bond1 > /sys/class/net/bonding_masters done One fix would be to check all callers and prevent concurrent calls to shrink_dcache_parent(). But I think a better solution is to stop the stealing behavior. This patch adds a new dentry flag that is set when the dentry is added to the dispose list. The flag is cleared in dentry_lru_del() in case the dentry gets a new reference just before being pruned. If the dentry has this flag, select_parent() will skip it and let shrink_dentry_list() retry pruning it. With select_parent() skipping those dentries there will not be the appearance of progress (new dentries found) when there is none, hence shrink_dcache_parent() will not loop forever. Set the flag is also set in prune_dcache_sb() for consistency as suggested by Linus. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> CC: stable@vger.kernel.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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f4947fbce2
Коммит
eaf5f90735
17
fs/dcache.c
17
fs/dcache.c
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@ -243,6 +243,7 @@ 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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@ -806,6 +807,7 @@ 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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@ -1097,14 +1099,19 @@ 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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dentry_lru_move_list(dentry, dispose);
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found++;
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} else {
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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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}
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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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@ -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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