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c27d82f52f
When superblock has lots of inodes without any pagecache (like is the case for /proc), drop_pagecache_sb() will iterate through all of them without dropping sb->s_inode_list_lock which can lead to softlockups (one of our customers hit this). Fix the problem by going to the slow path and doing cond_resched() in case the process needs rescheduling. Link: http://lkml.kernel.org/r/20190114085343.15011-1-jack@suse.cz Signed-off-by: Jan Kara <jack@suse.cz> Acked-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
77 lines
1.8 KiB
C
77 lines
1.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Implement the manual drop-all-pagecache function
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*/
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/fs.h>
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#include <linux/writeback.h>
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#include <linux/sysctl.h>
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#include <linux/gfp.h>
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#include "internal.h"
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/* A global variable is a bit ugly, but it keeps the code simple */
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int sysctl_drop_caches;
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static void drop_pagecache_sb(struct super_block *sb, void *unused)
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{
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struct inode *inode, *toput_inode = NULL;
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spin_lock(&sb->s_inode_list_lock);
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list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
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spin_lock(&inode->i_lock);
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/*
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* We must skip inodes in unusual state. We may also skip
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* inodes without pages but we deliberately won't in case
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* we need to reschedule to avoid softlockups.
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*/
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if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
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(inode->i_mapping->nrpages == 0 && !need_resched())) {
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spin_unlock(&inode->i_lock);
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continue;
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}
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__iget(inode);
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spin_unlock(&inode->i_lock);
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spin_unlock(&sb->s_inode_list_lock);
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cond_resched();
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invalidate_mapping_pages(inode->i_mapping, 0, -1);
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iput(toput_inode);
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toput_inode = inode;
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spin_lock(&sb->s_inode_list_lock);
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}
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spin_unlock(&sb->s_inode_list_lock);
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iput(toput_inode);
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}
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int drop_caches_sysctl_handler(struct ctl_table *table, int write,
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void __user *buffer, size_t *length, loff_t *ppos)
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{
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int ret;
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ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
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if (ret)
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return ret;
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if (write) {
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static int stfu;
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if (sysctl_drop_caches & 1) {
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iterate_supers(drop_pagecache_sb, NULL);
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count_vm_event(DROP_PAGECACHE);
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}
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if (sysctl_drop_caches & 2) {
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drop_slab();
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count_vm_event(DROP_SLAB);
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}
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if (!stfu) {
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pr_info("%s (%d): drop_caches: %d\n",
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current->comm, task_pid_nr(current),
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sysctl_drop_caches);
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}
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stfu |= sysctl_drop_caches & 4;
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}
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return 0;
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}
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