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Bit-spinlocks are problematic on PREEMPT_RT if functions which might sleep on RT, e.g. spin_lock(), alloc/free(), are invoked inside the lock held region because bit spinlocks disable preemption even on RT. A first attempt was to replace state lock with a spinlock placed in struct buffer_head and make the locking conditional on PREEMPT_RT and DEBUG_BIT_SPINLOCKS. Jan pointed out that there is a 4 byte hole in struct journal_head where a regular spinlock fits in and he would not object to convert the state lock to a spinlock unconditionally. Aside of solving the RT problem, this also gains lockdep coverage for the journal head state lock (bit-spinlocks are not covered by lockdep as it's hard to fit a lockdep map into a single bit). The trivial change would have been to convert the jbd_*lock_bh_state() inlines, but that comes with the downside that these functions take a buffer head pointer which needs to be converted to a journal head pointer which adds another level of indirection. As almost all functions which use this lock have a journal head pointer readily available, it makes more sense to remove the lock helper inlines and write out spin_*lock() at all call sites. Fixup all locking comments as well. Suggested-by: Jan Kara <jack@suse.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Jan Kara <jack@suse.cz> Cc: "Theodore Ts'o" <tytso@mit.edu> Cc: Mark Fasheh <mark@fasheh.com> Cc: Joseph Qi <joseph.qi@linux.alibaba.com> Cc: Joel Becker <jlbec@evilplan.org> Cc: Jan Kara <jack@suse.com> Cc: linux-ext4@vger.kernel.org Link: https://lore.kernel.org/r/20190809124233.13277-7-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
115 lines
2.9 KiB
C
115 lines
2.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* include/linux/journal-head.h
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*
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* buffer_head fields for JBD
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*
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* 27 May 2001 Andrew Morton
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* Created - pulled out of fs.h
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*/
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#ifndef JOURNAL_HEAD_H_INCLUDED
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#define JOURNAL_HEAD_H_INCLUDED
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#include <linux/spinlock.h>
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typedef unsigned int tid_t; /* Unique transaction ID */
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typedef struct transaction_s transaction_t; /* Compound transaction type */
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struct buffer_head;
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struct journal_head {
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/*
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* Points back to our buffer_head. [jbd_lock_bh_journal_head()]
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*/
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struct buffer_head *b_bh;
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/*
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* Protect the buffer head state
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*/
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spinlock_t b_state_lock;
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/*
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* Reference count - see description in journal.c
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* [jbd_lock_bh_journal_head()]
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*/
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int b_jcount;
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/*
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* Journalling list for this buffer [b_state_lock]
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* NOTE: We *cannot* combine this with b_modified into a bitfield
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* as gcc would then (which the C standard allows but which is
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* very unuseful) make 64-bit accesses to the bitfield and clobber
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* b_jcount if its update races with bitfield modification.
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*/
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unsigned b_jlist;
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/*
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* This flag signals the buffer has been modified by
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* the currently running transaction
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* [b_state_lock]
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*/
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unsigned b_modified;
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/*
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* Copy of the buffer data frozen for writing to the log.
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* [b_state_lock]
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*/
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char *b_frozen_data;
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/*
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* Pointer to a saved copy of the buffer containing no uncommitted
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* deallocation references, so that allocations can avoid overwriting
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* uncommitted deletes. [b_state_lock]
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*/
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char *b_committed_data;
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/*
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* Pointer to the compound transaction which owns this buffer's
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* metadata: either the running transaction or the committing
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* transaction (if there is one). Only applies to buffers on a
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* transaction's data or metadata journaling list.
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* [j_list_lock] [b_state_lock]
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* Either of these locks is enough for reading, both are needed for
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* changes.
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*/
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transaction_t *b_transaction;
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/*
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* Pointer to the running compound transaction which is currently
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* modifying the buffer's metadata, if there was already a transaction
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* committing it when the new transaction touched it.
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* [t_list_lock] [b_state_lock]
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*/
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transaction_t *b_next_transaction;
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/*
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* Doubly-linked list of buffers on a transaction's data, metadata or
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* forget queue. [t_list_lock] [b_state_lock]
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*/
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struct journal_head *b_tnext, *b_tprev;
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/*
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* Pointer to the compound transaction against which this buffer
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* is checkpointed. Only dirty buffers can be checkpointed.
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* [j_list_lock]
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*/
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transaction_t *b_cp_transaction;
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/*
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* Doubly-linked list of buffers still remaining to be flushed
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* before an old transaction can be checkpointed.
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* [j_list_lock]
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*/
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struct journal_head *b_cpnext, *b_cpprev;
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/* Trigger type */
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struct jbd2_buffer_trigger_type *b_triggers;
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/* Trigger type for the committing transaction's frozen data */
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struct jbd2_buffer_trigger_type *b_frozen_triggers;
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};
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#endif /* JOURNAL_HEAD_H_INCLUDED */
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