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13ae04d8d4
While stress-testing online repair of btrees, I noticed periodic
assertion failures from the buffer cache about buffers with incorrect
DELWRI_Q state. Looking further, I observed this race between the AIL
trying to write out a btree block and repair zapping a btree block after
the fact:
AIL: Repair0:
pin buffer X
delwri_queue:
set DELWRI_Q
add to delwri list
stale buf X:
clear DELWRI_Q
does not clear b_list
free space X
commit
delwri_submit # oops
Worse yet, I discovered that running the same repair over and over in a
tight loop can result in a second race that cause data integrity
problems with the repair:
AIL: Repair0: Repair1:
pin buffer X
delwri_queue:
set DELWRI_Q
add to delwri list
stale buf X:
clear DELWRI_Q
does not clear b_list
free space X
commit
find free space X
get buffer
rewrite buffer
delwri_queue:
set DELWRI_Q
already on a list, do not add
commit
BAD: committed tree root before all blocks written
delwri_submit # too late now
I traced this to my own misunderstanding of how the delwri lists work,
particularly with regards to the AIL's buffer list. If a buffer is
logged and committed, the buffer can end up on that AIL buffer list. If
btree repairs are run twice in rapid succession, it's possible that the
first repair will invalidate the buffer and free it before the next time
the AIL wakes up. Marking the buffer stale clears DELWRI_Q from the
buffer state without removing the buffer from its delwri list. The
buffer doesn't know which list it's on, so it cannot know which lock to
take to protect the list for a removal.
If the second repair allocates the same block, it will then recycle the
buffer to start writing the new btree block. Meanwhile, if the AIL
wakes up and walks the buffer list, it will ignore the buffer because it
can't lock it, and go back to sleep.
When the second repair calls delwri_queue to put the buffer on the
list of buffers to write before committing the new btree, it will set
DELWRI_Q again, but since the buffer hasn't been removed from the AIL's
buffer list, it won't add it to the bulkload buffer's list.
This is incorrect, because the bulkload caller relies on delwri_submit
to ensure that all the buffers have been sent to disk /before/
committing the new btree root pointer. This ordering requirement is
required for data consistency.
Worse, the AIL won't clear DELWRI_Q from the buffer when it does finally
drop it, so the next thread to walk through the btree will trip over a
debug assertion on that flag.
To fix this, create a new function that waits for the buffer to be
removed from any other delwri lists before adding the buffer to the
caller's delwri list. By waiting for the buffer to clear both the
delwri list and any potential delwri wait list, we can be sure that
repair will initiate writes of all buffers and report all write errors
back to userspace instead of committing the new structure.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
383 lines
12 KiB
C
383 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (c) 2000-2005 Silicon Graphics, Inc.
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* All Rights Reserved.
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*/
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#ifndef __XFS_BUF_H__
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#define __XFS_BUF_H__
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#include <linux/list.h>
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#include <linux/types.h>
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#include <linux/spinlock.h>
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#include <linux/mm.h>
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#include <linux/fs.h>
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#include <linux/dax.h>
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#include <linux/uio.h>
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#include <linux/list_lru.h>
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extern struct kmem_cache *xfs_buf_cache;
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/*
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* Base types
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*/
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struct xfs_buf;
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#define XFS_BUF_DADDR_NULL ((xfs_daddr_t) (-1LL))
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#define XBF_READ (1u << 0) /* buffer intended for reading from device */
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#define XBF_WRITE (1u << 1) /* buffer intended for writing to device */
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#define XBF_READ_AHEAD (1u << 2) /* asynchronous read-ahead */
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#define XBF_NO_IOACCT (1u << 3) /* bypass I/O accounting (non-LRU bufs) */
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#define XBF_ASYNC (1u << 4) /* initiator will not wait for completion */
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#define XBF_DONE (1u << 5) /* all pages in the buffer uptodate */
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#define XBF_STALE (1u << 6) /* buffer has been staled, do not find it */
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#define XBF_WRITE_FAIL (1u << 7) /* async writes have failed on this buffer */
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/* buffer type flags for write callbacks */
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#define _XBF_INODES (1u << 16)/* inode buffer */
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#define _XBF_DQUOTS (1u << 17)/* dquot buffer */
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#define _XBF_LOGRECOVERY (1u << 18)/* log recovery buffer */
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/* flags used only internally */
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#define _XBF_PAGES (1u << 20)/* backed by refcounted pages */
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#define _XBF_KMEM (1u << 21)/* backed by heap memory */
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#define _XBF_DELWRI_Q (1u << 22)/* buffer on a delwri queue */
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/* flags used only as arguments to access routines */
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/*
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* Online fsck is scanning the buffer cache for live buffers. Do not warn
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* about length mismatches during lookups and do not return stale buffers.
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*/
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#define XBF_LIVESCAN (1u << 28)
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#define XBF_INCORE (1u << 29)/* lookup only, return if found in cache */
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#define XBF_TRYLOCK (1u << 30)/* lock requested, but do not wait */
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#define XBF_UNMAPPED (1u << 31)/* do not map the buffer */
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typedef unsigned int xfs_buf_flags_t;
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#define XFS_BUF_FLAGS \
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{ XBF_READ, "READ" }, \
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{ XBF_WRITE, "WRITE" }, \
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{ XBF_READ_AHEAD, "READ_AHEAD" }, \
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{ XBF_NO_IOACCT, "NO_IOACCT" }, \
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{ XBF_ASYNC, "ASYNC" }, \
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{ XBF_DONE, "DONE" }, \
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{ XBF_STALE, "STALE" }, \
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{ XBF_WRITE_FAIL, "WRITE_FAIL" }, \
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{ _XBF_INODES, "INODES" }, \
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{ _XBF_DQUOTS, "DQUOTS" }, \
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{ _XBF_LOGRECOVERY, "LOG_RECOVERY" }, \
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{ _XBF_PAGES, "PAGES" }, \
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{ _XBF_KMEM, "KMEM" }, \
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{ _XBF_DELWRI_Q, "DELWRI_Q" }, \
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/* The following interface flags should never be set */ \
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{ XBF_LIVESCAN, "LIVESCAN" }, \
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{ XBF_INCORE, "INCORE" }, \
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{ XBF_TRYLOCK, "TRYLOCK" }, \
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{ XBF_UNMAPPED, "UNMAPPED" }
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/*
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* Internal state flags.
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*/
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#define XFS_BSTATE_DISPOSE (1 << 0) /* buffer being discarded */
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#define XFS_BSTATE_IN_FLIGHT (1 << 1) /* I/O in flight */
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/*
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* The xfs_buftarg contains 2 notions of "sector size" -
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*
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* 1) The metadata sector size, which is the minimum unit and
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* alignment of IO which will be performed by metadata operations.
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* 2) The device logical sector size
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*
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* The first is specified at mkfs time, and is stored on-disk in the
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* superblock's sb_sectsize.
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*
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* The latter is derived from the underlying device, and controls direct IO
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* alignment constraints.
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*/
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typedef struct xfs_buftarg {
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dev_t bt_dev;
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struct bdev_handle *bt_bdev_handle;
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struct block_device *bt_bdev;
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struct dax_device *bt_daxdev;
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u64 bt_dax_part_off;
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struct xfs_mount *bt_mount;
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unsigned int bt_meta_sectorsize;
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size_t bt_meta_sectormask;
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size_t bt_logical_sectorsize;
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size_t bt_logical_sectormask;
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/* LRU control structures */
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struct shrinker *bt_shrinker;
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struct list_lru bt_lru;
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struct percpu_counter bt_io_count;
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struct ratelimit_state bt_ioerror_rl;
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} xfs_buftarg_t;
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#define XB_PAGES 2
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struct xfs_buf_map {
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xfs_daddr_t bm_bn; /* block number for I/O */
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int bm_len; /* size of I/O */
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unsigned int bm_flags;
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};
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/*
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* Online fsck is scanning the buffer cache for live buffers. Do not warn
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* about length mismatches during lookups and do not return stale buffers.
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*/
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#define XBM_LIVESCAN (1U << 0)
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#define DEFINE_SINGLE_BUF_MAP(map, blkno, numblk) \
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struct xfs_buf_map (map) = { .bm_bn = (blkno), .bm_len = (numblk) };
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struct xfs_buf_ops {
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char *name;
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union {
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__be32 magic[2]; /* v4 and v5 on disk magic values */
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__be16 magic16[2]; /* v4 and v5 on disk magic values */
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};
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void (*verify_read)(struct xfs_buf *);
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void (*verify_write)(struct xfs_buf *);
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xfs_failaddr_t (*verify_struct)(struct xfs_buf *bp);
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};
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struct xfs_buf {
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/*
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* first cacheline holds all the fields needed for an uncontended cache
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* hit to be fully processed. The semaphore straddles the cacheline
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* boundary, but the counter and lock sits on the first cacheline,
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* which is the only bit that is touched if we hit the semaphore
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* fast-path on locking.
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*/
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struct rhash_head b_rhash_head; /* pag buffer hash node */
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xfs_daddr_t b_rhash_key; /* buffer cache index */
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int b_length; /* size of buffer in BBs */
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atomic_t b_hold; /* reference count */
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atomic_t b_lru_ref; /* lru reclaim ref count */
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xfs_buf_flags_t b_flags; /* status flags */
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struct semaphore b_sema; /* semaphore for lockables */
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/*
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* concurrent access to b_lru and b_lru_flags are protected by
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* bt_lru_lock and not by b_sema
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*/
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struct list_head b_lru; /* lru list */
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spinlock_t b_lock; /* internal state lock */
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unsigned int b_state; /* internal state flags */
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int b_io_error; /* internal IO error state */
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wait_queue_head_t b_waiters; /* unpin waiters */
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struct list_head b_list;
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struct xfs_perag *b_pag; /* contains rbtree root */
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struct xfs_mount *b_mount;
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struct xfs_buftarg *b_target; /* buffer target (device) */
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void *b_addr; /* virtual address of buffer */
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struct work_struct b_ioend_work;
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struct completion b_iowait; /* queue for I/O waiters */
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struct xfs_buf_log_item *b_log_item;
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struct list_head b_li_list; /* Log items list head */
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struct xfs_trans *b_transp;
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struct page **b_pages; /* array of page pointers */
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struct page *b_page_array[XB_PAGES]; /* inline pages */
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struct xfs_buf_map *b_maps; /* compound buffer map */
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struct xfs_buf_map __b_map; /* inline compound buffer map */
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int b_map_count;
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atomic_t b_pin_count; /* pin count */
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atomic_t b_io_remaining; /* #outstanding I/O requests */
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unsigned int b_page_count; /* size of page array */
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unsigned int b_offset; /* page offset of b_addr,
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only for _XBF_KMEM buffers */
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int b_error; /* error code on I/O */
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/*
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* async write failure retry count. Initialised to zero on the first
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* failure, then when it exceeds the maximum configured without a
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* success the write is considered to be failed permanently and the
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* iodone handler will take appropriate action.
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*
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* For retry timeouts, we record the jiffie of the first failure. This
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* means that we can change the retry timeout for buffers already under
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* I/O and thus avoid getting stuck in a retry loop with a long timeout.
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*
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* last_error is used to ensure that we are getting repeated errors, not
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* different errors. e.g. a block device might change ENOSPC to EIO when
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* a failure timeout occurs, so we want to re-initialise the error
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* retry behaviour appropriately when that happens.
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*/
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int b_retries;
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unsigned long b_first_retry_time; /* in jiffies */
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int b_last_error;
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const struct xfs_buf_ops *b_ops;
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struct rcu_head b_rcu;
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};
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/* Finding and Reading Buffers */
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int xfs_buf_get_map(struct xfs_buftarg *target, struct xfs_buf_map *map,
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int nmaps, xfs_buf_flags_t flags, struct xfs_buf **bpp);
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int xfs_buf_read_map(struct xfs_buftarg *target, struct xfs_buf_map *map,
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int nmaps, xfs_buf_flags_t flags, struct xfs_buf **bpp,
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const struct xfs_buf_ops *ops, xfs_failaddr_t fa);
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void xfs_buf_readahead_map(struct xfs_buftarg *target,
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struct xfs_buf_map *map, int nmaps,
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const struct xfs_buf_ops *ops);
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static inline int
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xfs_buf_incore(
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struct xfs_buftarg *target,
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xfs_daddr_t blkno,
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size_t numblks,
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xfs_buf_flags_t flags,
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struct xfs_buf **bpp)
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{
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DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
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return xfs_buf_get_map(target, &map, 1, XBF_INCORE | flags, bpp);
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}
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static inline int
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xfs_buf_get(
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struct xfs_buftarg *target,
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xfs_daddr_t blkno,
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size_t numblks,
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struct xfs_buf **bpp)
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{
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DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
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return xfs_buf_get_map(target, &map, 1, 0, bpp);
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}
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static inline int
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xfs_buf_read(
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struct xfs_buftarg *target,
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xfs_daddr_t blkno,
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size_t numblks,
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xfs_buf_flags_t flags,
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struct xfs_buf **bpp,
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const struct xfs_buf_ops *ops)
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{
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DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
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return xfs_buf_read_map(target, &map, 1, flags, bpp, ops,
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__builtin_return_address(0));
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}
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static inline void
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xfs_buf_readahead(
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struct xfs_buftarg *target,
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xfs_daddr_t blkno,
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size_t numblks,
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const struct xfs_buf_ops *ops)
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{
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DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
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return xfs_buf_readahead_map(target, &map, 1, ops);
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}
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int xfs_buf_get_uncached(struct xfs_buftarg *target, size_t numblks,
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xfs_buf_flags_t flags, struct xfs_buf **bpp);
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int xfs_buf_read_uncached(struct xfs_buftarg *target, xfs_daddr_t daddr,
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size_t numblks, xfs_buf_flags_t flags, struct xfs_buf **bpp,
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const struct xfs_buf_ops *ops);
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int _xfs_buf_read(struct xfs_buf *bp, xfs_buf_flags_t flags);
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void xfs_buf_hold(struct xfs_buf *bp);
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/* Releasing Buffers */
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extern void xfs_buf_rele(struct xfs_buf *);
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/* Locking and Unlocking Buffers */
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extern int xfs_buf_trylock(struct xfs_buf *);
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extern void xfs_buf_lock(struct xfs_buf *);
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extern void xfs_buf_unlock(struct xfs_buf *);
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#define xfs_buf_islocked(bp) \
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((bp)->b_sema.count <= 0)
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static inline void xfs_buf_relse(struct xfs_buf *bp)
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{
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xfs_buf_unlock(bp);
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xfs_buf_rele(bp);
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}
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/* Buffer Read and Write Routines */
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extern int xfs_bwrite(struct xfs_buf *bp);
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extern void __xfs_buf_ioerror(struct xfs_buf *bp, int error,
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xfs_failaddr_t failaddr);
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#define xfs_buf_ioerror(bp, err) __xfs_buf_ioerror((bp), (err), __this_address)
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extern void xfs_buf_ioerror_alert(struct xfs_buf *bp, xfs_failaddr_t fa);
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void xfs_buf_ioend_fail(struct xfs_buf *);
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void xfs_buf_zero(struct xfs_buf *bp, size_t boff, size_t bsize);
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void __xfs_buf_mark_corrupt(struct xfs_buf *bp, xfs_failaddr_t fa);
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#define xfs_buf_mark_corrupt(bp) __xfs_buf_mark_corrupt((bp), __this_address)
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/* Buffer Utility Routines */
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extern void *xfs_buf_offset(struct xfs_buf *, size_t);
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extern void xfs_buf_stale(struct xfs_buf *bp);
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/* Delayed Write Buffer Routines */
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extern void xfs_buf_delwri_cancel(struct list_head *);
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extern bool xfs_buf_delwri_queue(struct xfs_buf *, struct list_head *);
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void xfs_buf_delwri_queue_here(struct xfs_buf *bp, struct list_head *bl);
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extern int xfs_buf_delwri_submit(struct list_head *);
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extern int xfs_buf_delwri_submit_nowait(struct list_head *);
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extern int xfs_buf_delwri_pushbuf(struct xfs_buf *, struct list_head *);
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static inline xfs_daddr_t xfs_buf_daddr(struct xfs_buf *bp)
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{
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return bp->b_maps[0].bm_bn;
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}
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void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref);
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/*
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* If the buffer is already on the LRU, do nothing. Otherwise set the buffer
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* up with a reference count of 0 so it will be tossed from the cache when
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* released.
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*/
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static inline void xfs_buf_oneshot(struct xfs_buf *bp)
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{
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if (!list_empty(&bp->b_lru) || atomic_read(&bp->b_lru_ref) > 1)
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return;
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atomic_set(&bp->b_lru_ref, 0);
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}
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static inline int xfs_buf_ispinned(struct xfs_buf *bp)
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{
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return atomic_read(&bp->b_pin_count);
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}
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static inline int
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xfs_buf_verify_cksum(struct xfs_buf *bp, unsigned long cksum_offset)
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{
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return xfs_verify_cksum(bp->b_addr, BBTOB(bp->b_length),
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cksum_offset);
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}
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static inline void
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xfs_buf_update_cksum(struct xfs_buf *bp, unsigned long cksum_offset)
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{
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xfs_update_cksum(bp->b_addr, BBTOB(bp->b_length),
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cksum_offset);
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}
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/*
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* Handling of buftargs.
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*/
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struct xfs_buftarg *xfs_alloc_buftarg(struct xfs_mount *mp,
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struct bdev_handle *bdev_handle);
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extern void xfs_free_buftarg(struct xfs_buftarg *);
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extern void xfs_buftarg_wait(struct xfs_buftarg *);
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extern void xfs_buftarg_drain(struct xfs_buftarg *);
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extern int xfs_setsize_buftarg(struct xfs_buftarg *, unsigned int);
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#define xfs_getsize_buftarg(buftarg) block_size((buftarg)->bt_bdev)
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#define xfs_readonly_buftarg(buftarg) bdev_read_only((buftarg)->bt_bdev)
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int xfs_buf_reverify(struct xfs_buf *bp, const struct xfs_buf_ops *ops);
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bool xfs_verify_magic(struct xfs_buf *bp, __be32 dmagic);
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bool xfs_verify_magic16(struct xfs_buf *bp, __be16 dmagic);
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#endif /* __XFS_BUF_H__ */
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