WSL2-Linux-Kernel/fs/xfs/xfs_extfree_item.h

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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2000,2005 Silicon Graphics, Inc.
* All Rights Reserved.
*/
#ifndef __XFS_EXTFREE_ITEM_H__
#define __XFS_EXTFREE_ITEM_H__
/* kernel only EFI/EFD definitions */
struct xfs_mount;
struct kmem_zone;
/*
* Max number of extents in fast allocation path.
*/
#define XFS_EFI_MAX_FAST_EXTENTS 16
/*
xfs: don't free EFIs before the EFDs are committed Filesystems are occasionally being shut down with this error: xfs_trans_ail_delete_bulk: attempting to delete a log item that is not in the AIL. It was diagnosed to be related to the EFI/EFD commit order when the EFI and EFD are in different checkpoints and the EFD is committed before the EFI here: http://oss.sgi.com/archives/xfs/2013-01/msg00082.html The real problem is that a single bit cannot fully describe the states that the EFI/EFD processing can be in. These completion states are: EFI EFI in AIL EFD Result committed/unpinned Yes committed OK committed/pinned No committed Shutdown uncommitted No committed Shutdown Note that the "result" field is what should happen, not what does happen. The current logic is broken and handles the first two cases correctly by luck. That is, the code will free the EFI if the XFS_EFI_COMMITTED bit is *not* set, rather than if it is set. The inverted logic "works" because if both EFI and EFD are committed, then the first __xfs_efi_release() call clears the XFS_EFI_COMMITTED bit, and the second frees the EFI item. Hence as long as xfs_efi_item_committed() has been called, everything appears to be fine. It is the third case where the logic fails - where xfs_efd_item_committed() is called before xfs_efi_item_committed(), and that results in the EFI being freed before it has been committed. That is the bug that triggered the shutdown, and hence keeping track of whether the EFI has been committed or not is insufficient to correctly order the EFI/EFD operations w.r.t. the AIL. What we really want is this: the EFI is always placed into the AIL before the last reference goes away. The only way to guarantee that is that the EFI is not freed until after it has been unpinned *and* the EFD has been committed. That is, restructure the logic so that the only case that can occur is the first case. This can be done easily by replacing the XFS_EFI_COMMITTED with an EFI reference count. The EFI is initialised with it's own count, and that is not released until it is unpinned. However, there is a complication to this method - the high level EFI/EFD code in xfs_bmap_finish() does not hold direct references to the EFI structure, and runs a transaction commit between the EFI and EFD processing. Hence the EFI can be freed even before the EFD is created using such a method. Further, log recovery uses the AIL for tracking EFI/EFDs that need to be recovered, but it uses the AIL *differently* to the EFI transaction commit. Hence log recovery never pins or unpins EFIs, so we can't drop the EFI reference count indirectly to free the EFI. However, this doesn't prevent us from using a reference count here. There is a 1:1 relationship between EFIs and EFDs, so when we initialise the EFI we can take a reference count for the EFD as well. This solves the xfs_bmap_finish() issue - the EFI will never be freed until the EFD is processed. In terms of log recovery, during the committing of the EFD we can look for the XFS_EFI_RECOVERED bit being set and drop the EFI reference as well, thereby ensuring everything works correctly there as well. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Mark Tinguely <tinguely@sgi.com> Signed-off-by: Ben Myers <bpm@sgi.com>
2013-04-03 07:09:21 +04:00
* This is the "extent free intention" log item. It is used to log the fact
* that some extents need to be free. It is used in conjunction with the
* "extent free done" log item described below.
*
* The EFI is reference counted so that it is not freed prior to both the EFI
xfs: fix efi/efd error handling to avoid fs shutdown hangs Freeing an extent in XFS involves logging an EFI (extent free intention), freeing the actual extent, and logging an EFD (extent free done). The EFI object is created with a reference count of 2: one for the current transaction and one for the subsequently created EFD. Under normal circumstances, the first reference is dropped when the EFI is unpinned and the second reference is dropped when the EFD is committed to the on-disk log. In event of errors or filesystem shutdown, there are various potential cleanup scenarios depending on the state of the EFI/EFD. The cleanup scenarios are confusing and racy, as demonstrated by the following test sequence: # mount $dev $mnt # fsstress -d $mnt -n 99999 -p 16 -z -f fallocate=1 \ -f punch=1 -f creat=1 -f unlink=1 & # sleep 5 # killall -9 fsstress; wait # godown -f $mnt # umount ... in which the final umount can hang due to the AIL being pinned indefinitely by one or more EFI items. This can occur due to several conditions. For example, if the shutdown occurs after the EFI is committed to the on-disk log and the EFD committed to the CIL, but before the EFD committed to the log, the EFD iop_committed() abort handler does not drop its reference to the EFI. Alternatively, manual error injection in the xfs_bmap_finish() codepath shows that if an error occurs after the EFI transaction is committed but before the EFD is constructed and logged, the EFI is never released from the AIL. Update the EFI/EFD item handling code to use a more straightforward and reliable approach to error handling. If an error occurs after the EFI transaction is committed and before the EFD is constructed, release the EFI explicitly from xfs_bmap_finish(). If the EFI transaction is cancelled, release the EFI in the unlock handler. Once the EFD is constructed, it is responsible for releasing the EFI under any circumstances (including whether the EFI item aborts due to log I/O error). Update the EFD item handlers to release the EFI if the transaction is cancelled or aborts due to log I/O error. Finally, update xfs_bmap_finish() to log at least one EFD extent to the transaction before xfs_free_extent() errors are handled to ensure the transaction is dirty and EFD item error handling is triggered. Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>
2015-08-19 02:51:16 +03:00
* and EFD being committed and unpinned. This ensures the EFI is inserted into
* the AIL even in the event of out of order EFI/EFD processing. In other words,
* an EFI is born with two references:
*
* 1.) an EFI held reference to track EFI AIL insertion
* 2.) an EFD held reference to track EFD commit
*
* On allocation, both references are the responsibility of the caller. Once the
* EFI is added to and dirtied in a transaction, ownership of reference one
* transfers to the transaction. The reference is dropped once the EFI is
* inserted to the AIL or in the event of failure along the way (e.g., commit
* failure, log I/O error, etc.). Note that the caller remains responsible for
* the EFD reference under all circumstances to this point. The caller has no
* means to detect failure once the transaction is committed, however.
* Therefore, an EFD is required after this point, even in the event of
* unrelated failure.
*
* Once an EFD is allocated and dirtied in a transaction, reference two
* transfers to the transaction. The EFD reference is dropped once it reaches
* the unpin handler. Similar to the EFI, the reference also drops in the event
* of commit failure or log I/O errors. Note that the EFD is not inserted in the
* AIL, so at this point both the EFI and EFD are freed.
*/
struct xfs_efi_log_item {
struct xfs_log_item efi_item;
xfs: don't free EFIs before the EFDs are committed Filesystems are occasionally being shut down with this error: xfs_trans_ail_delete_bulk: attempting to delete a log item that is not in the AIL. It was diagnosed to be related to the EFI/EFD commit order when the EFI and EFD are in different checkpoints and the EFD is committed before the EFI here: http://oss.sgi.com/archives/xfs/2013-01/msg00082.html The real problem is that a single bit cannot fully describe the states that the EFI/EFD processing can be in. These completion states are: EFI EFI in AIL EFD Result committed/unpinned Yes committed OK committed/pinned No committed Shutdown uncommitted No committed Shutdown Note that the "result" field is what should happen, not what does happen. The current logic is broken and handles the first two cases correctly by luck. That is, the code will free the EFI if the XFS_EFI_COMMITTED bit is *not* set, rather than if it is set. The inverted logic "works" because if both EFI and EFD are committed, then the first __xfs_efi_release() call clears the XFS_EFI_COMMITTED bit, and the second frees the EFI item. Hence as long as xfs_efi_item_committed() has been called, everything appears to be fine. It is the third case where the logic fails - where xfs_efd_item_committed() is called before xfs_efi_item_committed(), and that results in the EFI being freed before it has been committed. That is the bug that triggered the shutdown, and hence keeping track of whether the EFI has been committed or not is insufficient to correctly order the EFI/EFD operations w.r.t. the AIL. What we really want is this: the EFI is always placed into the AIL before the last reference goes away. The only way to guarantee that is that the EFI is not freed until after it has been unpinned *and* the EFD has been committed. That is, restructure the logic so that the only case that can occur is the first case. This can be done easily by replacing the XFS_EFI_COMMITTED with an EFI reference count. The EFI is initialised with it's own count, and that is not released until it is unpinned. However, there is a complication to this method - the high level EFI/EFD code in xfs_bmap_finish() does not hold direct references to the EFI structure, and runs a transaction commit between the EFI and EFD processing. Hence the EFI can be freed even before the EFD is created using such a method. Further, log recovery uses the AIL for tracking EFI/EFDs that need to be recovered, but it uses the AIL *differently* to the EFI transaction commit. Hence log recovery never pins or unpins EFIs, so we can't drop the EFI reference count indirectly to free the EFI. However, this doesn't prevent us from using a reference count here. There is a 1:1 relationship between EFIs and EFDs, so when we initialise the EFI we can take a reference count for the EFD as well. This solves the xfs_bmap_finish() issue - the EFI will never be freed until the EFD is processed. In terms of log recovery, during the committing of the EFD we can look for the XFS_EFI_RECOVERED bit being set and drop the EFI reference as well, thereby ensuring everything works correctly there as well. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Mark Tinguely <tinguely@sgi.com> Signed-off-by: Ben Myers <bpm@sgi.com>
2013-04-03 07:09:21 +04:00
atomic_t efi_refcount;
atomic_t efi_next_extent;
xfs_efi_log_format_t efi_format;
};
/*
* This is the "extent free done" log item. It is used to log
* the fact that some extents earlier mentioned in an efi item
* have been freed.
*/
struct xfs_efd_log_item {
struct xfs_log_item efd_item;
struct xfs_efi_log_item *efd_efip;
uint efd_next_extent;
xfs_efd_log_format_t efd_format;
};
/*
* Max number of extents in fast allocation path.
*/
#define XFS_EFD_MAX_FAST_EXTENTS 16
extern struct kmem_zone *xfs_efi_zone;
extern struct kmem_zone *xfs_efd_zone;
#endif /* __XFS_EXTFREE_ITEM_H__ */