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![Greg Thelen](/assets/img/avatar_default.png)
lock_page_memcg()/unlock_page_memcg() use spin_lock_irqsave/restore() if
the page's memcg is undergoing move accounting, which occurs when a
process leaves its memcg for a new one that has
memory.move_charge_at_immigrate set.
unlocked_inode_to_wb_begin,end() use spin_lock_irq/spin_unlock_irq() if
the given inode is switching writeback domains. Switches occur when
enough writes are issued from a new domain.
This existing pattern is thus suspicious:
lock_page_memcg(page);
unlocked_inode_to_wb_begin(inode, &locked);
...
unlocked_inode_to_wb_end(inode, locked);
unlock_page_memcg(page);
If both inode switch and process memcg migration are both in-flight then
unlocked_inode_to_wb_end() will unconditionally enable interrupts while
still holding the lock_page_memcg() irq spinlock. This suggests the
possibility of deadlock if an interrupt occurs before unlock_page_memcg().
truncate
__cancel_dirty_page
lock_page_memcg
unlocked_inode_to_wb_begin
unlocked_inode_to_wb_end
<interrupts mistakenly enabled>
<interrupt>
end_page_writeback
test_clear_page_writeback
lock_page_memcg
<deadlock>
unlock_page_memcg
Due to configuration limitations this deadlock is not currently possible
because we don't mix cgroup writeback (a cgroupv2 feature) and
memory.move_charge_at_immigrate (a cgroupv1 feature).
If the kernel is hacked to always claim inode switching and memcg
moving_account, then this script triggers lockup in less than a minute:
cd /mnt/cgroup/memory
mkdir a b
echo 1 > a/memory.move_charge_at_immigrate
echo 1 > b/memory.move_charge_at_immigrate
(
echo $BASHPID > a/cgroup.procs
while true; do
dd if=/dev/zero of=/mnt/big bs=1M count=256
done
) &
while true; do
sync
done &
sleep 1h &
SLEEP=$!
while true; do
echo $SLEEP > a/cgroup.procs
echo $SLEEP > b/cgroup.procs
done
The deadlock does not seem possible, so it's debatable if there's any
reason to modify the kernel. I suggest we should to prevent future
surprises. And Wang Long said "this deadlock occurs three times in our
environment", so there's more reason to apply this, even to stable.
Stable 4.4 has minor conflicts applying this patch. For a clean 4.4 patch
see "[PATCH for-4.4] writeback: safer lock nesting"
https://lkml.org/lkml/2018/4/11/146
Wang Long said "this deadlock occurs three times in our environment"
[gthelen@google.com: v4]
Link: http://lkml.kernel.org/r/20180411084653.254724-1-gthelen@google.com
[akpm@linux-foundation.org: comment tweaks, struct initialization simplification]
Change-Id: Ibb773e8045852978f6207074491d262f1b3fb613
Link: http://lkml.kernel.org/r/20180410005908.167976-1-gthelen@google.com
Fixes: 682aa8e1a6
("writeback: implement unlocked_inode_to_wb transaction and use it for stat updates")
Signed-off-by: Greg Thelen <gthelen@google.com>
Reported-by: Wang Long <wanglong19@meituan.com>
Acked-by: Wang Long <wanglong19@meituan.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: <stable@vger.kernel.org> [v4.2+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
501 lines
14 KiB
C
501 lines
14 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* include/linux/backing-dev.h
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*
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* low-level device information and state which is propagated up through
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* to high-level code.
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*/
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#ifndef _LINUX_BACKING_DEV_H
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#define _LINUX_BACKING_DEV_H
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#include <linux/kernel.h>
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#include <linux/fs.h>
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#include <linux/sched.h>
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#include <linux/blkdev.h>
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#include <linux/writeback.h>
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#include <linux/blk-cgroup.h>
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#include <linux/backing-dev-defs.h>
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#include <linux/slab.h>
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static inline struct backing_dev_info *bdi_get(struct backing_dev_info *bdi)
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{
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kref_get(&bdi->refcnt);
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return bdi;
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}
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void bdi_put(struct backing_dev_info *bdi);
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__printf(2, 3)
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int bdi_register(struct backing_dev_info *bdi, const char *fmt, ...);
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__printf(2, 0)
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int bdi_register_va(struct backing_dev_info *bdi, const char *fmt,
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va_list args);
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int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner);
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void bdi_unregister(struct backing_dev_info *bdi);
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struct backing_dev_info *bdi_alloc_node(gfp_t gfp_mask, int node_id);
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static inline struct backing_dev_info *bdi_alloc(gfp_t gfp_mask)
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{
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return bdi_alloc_node(gfp_mask, NUMA_NO_NODE);
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}
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void wb_start_background_writeback(struct bdi_writeback *wb);
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void wb_workfn(struct work_struct *work);
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void wb_wakeup_delayed(struct bdi_writeback *wb);
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extern spinlock_t bdi_lock;
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extern struct list_head bdi_list;
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extern struct workqueue_struct *bdi_wq;
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static inline bool wb_has_dirty_io(struct bdi_writeback *wb)
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{
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return test_bit(WB_has_dirty_io, &wb->state);
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}
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static inline bool bdi_has_dirty_io(struct backing_dev_info *bdi)
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{
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/*
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* @bdi->tot_write_bandwidth is guaranteed to be > 0 if there are
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* any dirty wbs. See wb_update_write_bandwidth().
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*/
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return atomic_long_read(&bdi->tot_write_bandwidth);
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}
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static inline void __add_wb_stat(struct bdi_writeback *wb,
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enum wb_stat_item item, s64 amount)
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{
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percpu_counter_add_batch(&wb->stat[item], amount, WB_STAT_BATCH);
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}
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static inline void inc_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
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{
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__add_wb_stat(wb, item, 1);
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}
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static inline void dec_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
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{
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__add_wb_stat(wb, item, -1);
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}
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static inline s64 wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
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{
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return percpu_counter_read_positive(&wb->stat[item]);
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}
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static inline s64 wb_stat_sum(struct bdi_writeback *wb, enum wb_stat_item item)
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{
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return percpu_counter_sum_positive(&wb->stat[item]);
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}
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extern void wb_writeout_inc(struct bdi_writeback *wb);
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/*
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* maximal error of a stat counter.
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*/
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static inline unsigned long wb_stat_error(void)
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{
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#ifdef CONFIG_SMP
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return nr_cpu_ids * WB_STAT_BATCH;
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#else
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return 1;
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#endif
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}
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int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio);
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int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
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/*
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* Flags in backing_dev_info::capability
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*
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* The first three flags control whether dirty pages will contribute to the
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* VM's accounting and whether writepages() should be called for dirty pages
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* (something that would not, for example, be appropriate for ramfs)
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*
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* WARNING: these flags are closely related and should not normally be
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* used separately. The BDI_CAP_NO_ACCT_AND_WRITEBACK combines these
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* three flags into a single convenience macro.
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*
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* BDI_CAP_NO_ACCT_DIRTY: Dirty pages shouldn't contribute to accounting
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* BDI_CAP_NO_WRITEBACK: Don't write pages back
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* BDI_CAP_NO_ACCT_WB: Don't automatically account writeback pages
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* BDI_CAP_STRICTLIMIT: Keep number of dirty pages below bdi threshold.
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*
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* BDI_CAP_CGROUP_WRITEBACK: Supports cgroup-aware writeback.
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* BDI_CAP_SYNCHRONOUS_IO: Device is so fast that asynchronous IO would be
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* inefficient.
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*/
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#define BDI_CAP_NO_ACCT_DIRTY 0x00000001
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#define BDI_CAP_NO_WRITEBACK 0x00000002
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#define BDI_CAP_NO_ACCT_WB 0x00000004
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#define BDI_CAP_STABLE_WRITES 0x00000008
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#define BDI_CAP_STRICTLIMIT 0x00000010
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#define BDI_CAP_CGROUP_WRITEBACK 0x00000020
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#define BDI_CAP_SYNCHRONOUS_IO 0x00000040
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#define BDI_CAP_NO_ACCT_AND_WRITEBACK \
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(BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB)
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extern struct backing_dev_info noop_backing_dev_info;
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/**
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* writeback_in_progress - determine whether there is writeback in progress
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* @wb: bdi_writeback of interest
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*
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* Determine whether there is writeback waiting to be handled against a
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* bdi_writeback.
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*/
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static inline bool writeback_in_progress(struct bdi_writeback *wb)
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{
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return test_bit(WB_writeback_running, &wb->state);
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}
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static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
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{
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struct super_block *sb;
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if (!inode)
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return &noop_backing_dev_info;
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sb = inode->i_sb;
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#ifdef CONFIG_BLOCK
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if (sb_is_blkdev_sb(sb))
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return I_BDEV(inode)->bd_bdi;
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#endif
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return sb->s_bdi;
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}
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static inline int wb_congested(struct bdi_writeback *wb, int cong_bits)
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{
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struct backing_dev_info *bdi = wb->bdi;
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if (bdi->congested_fn)
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return bdi->congested_fn(bdi->congested_data, cong_bits);
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return wb->congested->state & cong_bits;
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}
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long congestion_wait(int sync, long timeout);
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long wait_iff_congested(int sync, long timeout);
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static inline bool bdi_cap_synchronous_io(struct backing_dev_info *bdi)
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{
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return bdi->capabilities & BDI_CAP_SYNCHRONOUS_IO;
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}
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static inline bool bdi_cap_stable_pages_required(struct backing_dev_info *bdi)
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{
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return bdi->capabilities & BDI_CAP_STABLE_WRITES;
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}
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static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
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{
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return !(bdi->capabilities & BDI_CAP_NO_WRITEBACK);
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}
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static inline bool bdi_cap_account_dirty(struct backing_dev_info *bdi)
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{
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return !(bdi->capabilities & BDI_CAP_NO_ACCT_DIRTY);
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}
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static inline bool bdi_cap_account_writeback(struct backing_dev_info *bdi)
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{
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/* Paranoia: BDI_CAP_NO_WRITEBACK implies BDI_CAP_NO_ACCT_WB */
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return !(bdi->capabilities & (BDI_CAP_NO_ACCT_WB |
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BDI_CAP_NO_WRITEBACK));
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}
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static inline bool mapping_cap_writeback_dirty(struct address_space *mapping)
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{
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return bdi_cap_writeback_dirty(inode_to_bdi(mapping->host));
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}
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static inline bool mapping_cap_account_dirty(struct address_space *mapping)
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{
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return bdi_cap_account_dirty(inode_to_bdi(mapping->host));
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}
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static inline int bdi_sched_wait(void *word)
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{
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schedule();
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return 0;
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}
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#ifdef CONFIG_CGROUP_WRITEBACK
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struct bdi_writeback_congested *
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wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp);
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void wb_congested_put(struct bdi_writeback_congested *congested);
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struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
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struct cgroup_subsys_state *memcg_css,
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gfp_t gfp);
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void wb_memcg_offline(struct mem_cgroup *memcg);
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void wb_blkcg_offline(struct blkcg *blkcg);
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int inode_congested(struct inode *inode, int cong_bits);
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/**
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* inode_cgwb_enabled - test whether cgroup writeback is enabled on an inode
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* @inode: inode of interest
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*
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* cgroup writeback requires support from both the bdi and filesystem.
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* Also, both memcg and iocg have to be on the default hierarchy. Test
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* whether all conditions are met.
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*
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* Note that the test result may change dynamically on the same inode
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* depending on how memcg and iocg are configured.
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*/
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static inline bool inode_cgwb_enabled(struct inode *inode)
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{
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struct backing_dev_info *bdi = inode_to_bdi(inode);
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return cgroup_subsys_on_dfl(memory_cgrp_subsys) &&
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cgroup_subsys_on_dfl(io_cgrp_subsys) &&
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bdi_cap_account_dirty(bdi) &&
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(bdi->capabilities & BDI_CAP_CGROUP_WRITEBACK) &&
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(inode->i_sb->s_iflags & SB_I_CGROUPWB);
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}
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/**
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* wb_find_current - find wb for %current on a bdi
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* @bdi: bdi of interest
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*
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* Find the wb of @bdi which matches both the memcg and blkcg of %current.
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* Must be called under rcu_read_lock() which protects the returend wb.
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* NULL if not found.
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*/
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static inline struct bdi_writeback *wb_find_current(struct backing_dev_info *bdi)
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{
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struct cgroup_subsys_state *memcg_css;
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struct bdi_writeback *wb;
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memcg_css = task_css(current, memory_cgrp_id);
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if (!memcg_css->parent)
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return &bdi->wb;
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wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
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/*
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* %current's blkcg equals the effective blkcg of its memcg. No
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* need to use the relatively expensive cgroup_get_e_css().
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*/
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if (likely(wb && wb->blkcg_css == task_css(current, io_cgrp_id)))
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return wb;
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return NULL;
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}
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/**
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* wb_get_create_current - get or create wb for %current on a bdi
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* @bdi: bdi of interest
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* @gfp: allocation mask
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*
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* Equivalent to wb_get_create() on %current's memcg. This function is
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* called from a relatively hot path and optimizes the common cases using
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* wb_find_current().
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*/
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static inline struct bdi_writeback *
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wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
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{
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struct bdi_writeback *wb;
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rcu_read_lock();
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wb = wb_find_current(bdi);
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if (wb && unlikely(!wb_tryget(wb)))
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wb = NULL;
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rcu_read_unlock();
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if (unlikely(!wb)) {
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struct cgroup_subsys_state *memcg_css;
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memcg_css = task_get_css(current, memory_cgrp_id);
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wb = wb_get_create(bdi, memcg_css, gfp);
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css_put(memcg_css);
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}
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return wb;
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}
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/**
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* inode_to_wb_is_valid - test whether an inode has a wb associated
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* @inode: inode of interest
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*
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* Returns %true if @inode has a wb associated. May be called without any
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* locking.
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*/
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static inline bool inode_to_wb_is_valid(struct inode *inode)
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{
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return inode->i_wb;
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}
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/**
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* inode_to_wb - determine the wb of an inode
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* @inode: inode of interest
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*
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* Returns the wb @inode is currently associated with. The caller must be
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* holding either @inode->i_lock, the i_pages lock, or the
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* associated wb's list_lock.
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*/
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static inline struct bdi_writeback *inode_to_wb(const struct inode *inode)
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{
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#ifdef CONFIG_LOCKDEP
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WARN_ON_ONCE(debug_locks &&
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(!lockdep_is_held(&inode->i_lock) &&
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!lockdep_is_held(&inode->i_mapping->i_pages.xa_lock) &&
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!lockdep_is_held(&inode->i_wb->list_lock)));
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#endif
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return inode->i_wb;
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}
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/**
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* unlocked_inode_to_wb_begin - begin unlocked inode wb access transaction
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* @inode: target inode
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* @cookie: output param, to be passed to the end function
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*
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* The caller wants to access the wb associated with @inode but isn't
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* holding inode->i_lock, the i_pages lock or wb->list_lock. This
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* function determines the wb associated with @inode and ensures that the
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* association doesn't change until the transaction is finished with
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* unlocked_inode_to_wb_end().
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*
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* The caller must call unlocked_inode_to_wb_end() with *@cookie afterwards and
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* can't sleep during the transaction. IRQs may or may not be disabled on
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* return.
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*/
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static inline struct bdi_writeback *
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unlocked_inode_to_wb_begin(struct inode *inode, struct wb_lock_cookie *cookie)
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{
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rcu_read_lock();
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/*
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* Paired with store_release in inode_switch_wb_work_fn() and
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* ensures that we see the new wb if we see cleared I_WB_SWITCH.
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*/
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cookie->locked = smp_load_acquire(&inode->i_state) & I_WB_SWITCH;
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if (unlikely(cookie->locked))
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xa_lock_irqsave(&inode->i_mapping->i_pages, cookie->flags);
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/*
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* Protected by either !I_WB_SWITCH + rcu_read_lock() or the i_pages
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* lock. inode_to_wb() will bark. Deref directly.
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*/
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return inode->i_wb;
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}
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/**
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* unlocked_inode_to_wb_end - end inode wb access transaction
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* @inode: target inode
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* @cookie: @cookie from unlocked_inode_to_wb_begin()
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*/
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static inline void unlocked_inode_to_wb_end(struct inode *inode,
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struct wb_lock_cookie *cookie)
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{
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if (unlikely(cookie->locked))
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xa_unlock_irqrestore(&inode->i_mapping->i_pages, cookie->flags);
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rcu_read_unlock();
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}
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#else /* CONFIG_CGROUP_WRITEBACK */
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static inline bool inode_cgwb_enabled(struct inode *inode)
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{
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return false;
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}
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static inline struct bdi_writeback_congested *
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wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
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{
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atomic_inc(&bdi->wb_congested->refcnt);
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return bdi->wb_congested;
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}
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static inline void wb_congested_put(struct bdi_writeback_congested *congested)
|
|
{
|
|
if (atomic_dec_and_test(&congested->refcnt))
|
|
kfree(congested);
|
|
}
|
|
|
|
static inline struct bdi_writeback *wb_find_current(struct backing_dev_info *bdi)
|
|
{
|
|
return &bdi->wb;
|
|
}
|
|
|
|
static inline struct bdi_writeback *
|
|
wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
|
|
{
|
|
return &bdi->wb;
|
|
}
|
|
|
|
static inline bool inode_to_wb_is_valid(struct inode *inode)
|
|
{
|
|
return true;
|
|
}
|
|
|
|
static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
|
|
{
|
|
return &inode_to_bdi(inode)->wb;
|
|
}
|
|
|
|
static inline struct bdi_writeback *
|
|
unlocked_inode_to_wb_begin(struct inode *inode, struct wb_lock_cookie *cookie)
|
|
{
|
|
return inode_to_wb(inode);
|
|
}
|
|
|
|
static inline void unlocked_inode_to_wb_end(struct inode *inode,
|
|
struct wb_lock_cookie *cookie)
|
|
{
|
|
}
|
|
|
|
static inline void wb_memcg_offline(struct mem_cgroup *memcg)
|
|
{
|
|
}
|
|
|
|
static inline void wb_blkcg_offline(struct blkcg *blkcg)
|
|
{
|
|
}
|
|
|
|
static inline int inode_congested(struct inode *inode, int cong_bits)
|
|
{
|
|
return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
|
|
}
|
|
|
|
#endif /* CONFIG_CGROUP_WRITEBACK */
|
|
|
|
static inline int inode_read_congested(struct inode *inode)
|
|
{
|
|
return inode_congested(inode, 1 << WB_sync_congested);
|
|
}
|
|
|
|
static inline int inode_write_congested(struct inode *inode)
|
|
{
|
|
return inode_congested(inode, 1 << WB_async_congested);
|
|
}
|
|
|
|
static inline int inode_rw_congested(struct inode *inode)
|
|
{
|
|
return inode_congested(inode, (1 << WB_sync_congested) |
|
|
(1 << WB_async_congested));
|
|
}
|
|
|
|
static inline int bdi_congested(struct backing_dev_info *bdi, int cong_bits)
|
|
{
|
|
return wb_congested(&bdi->wb, cong_bits);
|
|
}
|
|
|
|
static inline int bdi_read_congested(struct backing_dev_info *bdi)
|
|
{
|
|
return bdi_congested(bdi, 1 << WB_sync_congested);
|
|
}
|
|
|
|
static inline int bdi_write_congested(struct backing_dev_info *bdi)
|
|
{
|
|
return bdi_congested(bdi, 1 << WB_async_congested);
|
|
}
|
|
|
|
static inline int bdi_rw_congested(struct backing_dev_info *bdi)
|
|
{
|
|
return bdi_congested(bdi, (1 << WB_sync_congested) |
|
|
(1 << WB_async_congested));
|
|
}
|
|
|
|
#endif /* _LINUX_BACKING_DEV_H */
|