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xfs_log_cil.c
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xfs_log_cil.c
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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2010 Red Hat, Inc. All Rights Reserved.
*/
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_shared.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_extent_busy.h"
#include "xfs_trans.h"
#include "xfs_trans_priv.h"
#include "xfs_log.h"
#include "xfs_log_priv.h"
#include "xfs_trace.h"
struct workqueue_struct *xfs_discard_wq;
/*
* Allocate a new ticket. Failing to get a new ticket makes it really hard to
* recover, so we don't allow failure here. Also, we allocate in a context that
* we don't want to be issuing transactions from, so we need to tell the
* allocation code this as well.
*
* We don't reserve any space for the ticket - we are going to steal whatever
* space we require from transactions as they commit. To ensure we reserve all
* the space required, we need to set the current reservation of the ticket to
* zero so that we know to steal the initial transaction overhead from the
* first transaction commit.
*/
static struct xlog_ticket *
xlog_cil_ticket_alloc(
struct xlog *log)
{
struct xlog_ticket *tic;
tic = xlog_ticket_alloc(log, 0, 1, XFS_TRANSACTION, 0);
/*
* set the current reservation to zero so we know to steal the basic
* transaction overhead reservation from the first transaction commit.
*/
tic->t_curr_res = 0;
return tic;
}
/*
* After the first stage of log recovery is done, we know where the head and
* tail of the log are. We need this log initialisation done before we can
* initialise the first CIL checkpoint context.
*
* Here we allocate a log ticket to track space usage during a CIL push. This
* ticket is passed to xlog_write() directly so that we don't slowly leak log
* space by failing to account for space used by log headers and additional
* region headers for split regions.
*/
void
xlog_cil_init_post_recovery(
struct xlog *log)
{
log->l_cilp->xc_ctx->ticket = xlog_cil_ticket_alloc(log);
log->l_cilp->xc_ctx->sequence = 1;
}
static inline int
xlog_cil_iovec_space(
uint niovecs)
{
return round_up((sizeof(struct xfs_log_vec) +
niovecs * sizeof(struct xfs_log_iovec)),
sizeof(uint64_t));
}
/*
* Allocate or pin log vector buffers for CIL insertion.
*
* The CIL currently uses disposable buffers for copying a snapshot of the
* modified items into the log during a push. The biggest problem with this is
* the requirement to allocate the disposable buffer during the commit if:
* a) does not exist; or
* b) it is too small
*
* If we do this allocation within xlog_cil_insert_format_items(), it is done
* under the xc_ctx_lock, which means that a CIL push cannot occur during
* the memory allocation. This means that we have a potential deadlock situation
* under low memory conditions when we have lots of dirty metadata pinned in
* the CIL and we need a CIL commit to occur to free memory.
*
* To avoid this, we need to move the memory allocation outside the
* xc_ctx_lock, but because the log vector buffers are disposable, that opens
* up a TOCTOU race condition w.r.t. the CIL committing and removing the log
* vector buffers between the check and the formatting of the item into the
* log vector buffer within the xc_ctx_lock.
*
* Because the log vector buffer needs to be unchanged during the CIL push
* process, we cannot share the buffer between the transaction commit (which
* modifies the buffer) and the CIL push context that is writing the changes
* into the log. This means skipping preallocation of buffer space is
* unreliable, but we most definitely do not want to be allocating and freeing
* buffers unnecessarily during commits when overwrites can be done safely.
*
* The simplest solution to this problem is to allocate a shadow buffer when a
* log item is committed for the second time, and then to only use this buffer
* if necessary. The buffer can remain attached to the log item until such time
* it is needed, and this is the buffer that is reallocated to match the size of
* the incoming modification. Then during the formatting of the item we can swap
* the active buffer with the new one if we can't reuse the existing buffer. We
* don't free the old buffer as it may be reused on the next modification if
* it's size is right, otherwise we'll free and reallocate it at that point.
*
* This function builds a vector for the changes in each log item in the
* transaction. It then works out the length of the buffer needed for each log
* item, allocates them and attaches the vector to the log item in preparation
* for the formatting step which occurs under the xc_ctx_lock.
*
* While this means the memory footprint goes up, it avoids the repeated
* alloc/free pattern that repeated modifications of an item would otherwise
* cause, and hence minimises the CPU overhead of such behaviour.
*/
static void
xlog_cil_alloc_shadow_bufs(
struct xlog *log,
struct xfs_trans *tp)
{
struct xfs_log_item *lip;
list_for_each_entry(lip, &tp->t_items, li_trans) {
struct xfs_log_vec *lv;
int niovecs = 0;
int nbytes = 0;
int buf_size;
bool ordered = false;
/* Skip items which aren't dirty in this transaction. */
if (!test_bit(XFS_LI_DIRTY, &lip->li_flags))
continue;
/* get number of vecs and size of data to be stored */
lip->li_ops->iop_size(lip, &niovecs, &nbytes);
/*
* Ordered items need to be tracked but we do not wish to write
* them. We need a logvec to track the object, but we do not
* need an iovec or buffer to be allocated for copying data.
*/
if (niovecs == XFS_LOG_VEC_ORDERED) {
ordered = true;
niovecs = 0;
nbytes = 0;
}
/*
* We 64-bit align the length of each iovec so that the start
* of the next one is naturally aligned. We'll need to
* account for that slack space here. Then round nbytes up
* to 64-bit alignment so that the initial buffer alignment is
* easy to calculate and verify.
*/
nbytes += niovecs * sizeof(uint64_t);
nbytes = round_up(nbytes, sizeof(uint64_t));
/*
* The data buffer needs to start 64-bit aligned, so round up
* that space to ensure we can align it appropriately and not
* overrun the buffer.
*/
buf_size = nbytes + xlog_cil_iovec_space(niovecs);
/*
* if we have no shadow buffer, or it is too small, we need to
* reallocate it.
*/
if (!lip->li_lv_shadow ||
buf_size > lip->li_lv_shadow->lv_size) {
/*
* We free and allocate here as a realloc would copy
* unnecessary data. We don't use kmem_zalloc() for the
* same reason - we don't need to zero the data area in
* the buffer, only the log vector header and the iovec
* storage.
*/
kmem_free(lip->li_lv_shadow);
lv = kmem_alloc_large(buf_size, KM_NOFS);
memset(lv, 0, xlog_cil_iovec_space(niovecs));
lv->lv_item = lip;
lv->lv_size = buf_size;
if (ordered)
lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
else
lv->lv_iovecp = (struct xfs_log_iovec *)&lv[1];
lip->li_lv_shadow = lv;
} else {
/* same or smaller, optimise common overwrite case */
lv = lip->li_lv_shadow;
if (ordered)
lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
else
lv->lv_buf_len = 0;
lv->lv_bytes = 0;
lv->lv_next = NULL;
}
/* Ensure the lv is set up according to ->iop_size */
lv->lv_niovecs = niovecs;
/* The allocated data region lies beyond the iovec region */
lv->lv_buf = (char *)lv + xlog_cil_iovec_space(niovecs);
}
}
/*
* Prepare the log item for insertion into the CIL. Calculate the difference in
* log space and vectors it will consume, and if it is a new item pin it as
* well.
*/
STATIC void
xfs_cil_prepare_item(
struct xlog *log,
struct xfs_log_vec *lv,
struct xfs_log_vec *old_lv,
int *diff_len,
int *diff_iovecs)
{
/* Account for the new LV being passed in */
if (lv->lv_buf_len != XFS_LOG_VEC_ORDERED) {
*diff_len += lv->lv_bytes;
*diff_iovecs += lv->lv_niovecs;
}
/*
* If there is no old LV, this is the first time we've seen the item in
* this CIL context and so we need to pin it. If we are replacing the
* old_lv, then remove the space it accounts for and make it the shadow
* buffer for later freeing. In both cases we are now switching to the
* shadow buffer, so update the pointer to it appropriately.
*/
if (!old_lv) {
if (lv->lv_item->li_ops->iop_pin)
lv->lv_item->li_ops->iop_pin(lv->lv_item);
lv->lv_item->li_lv_shadow = NULL;
} else if (old_lv != lv) {
ASSERT(lv->lv_buf_len != XFS_LOG_VEC_ORDERED);
*diff_len -= old_lv->lv_bytes;
*diff_iovecs -= old_lv->lv_niovecs;
lv->lv_item->li_lv_shadow = old_lv;
}
/* attach new log vector to log item */
lv->lv_item->li_lv = lv;
/*
* If this is the first time the item is being committed to the
* CIL, store the sequence number on the log item so we can
* tell in future commits whether this is the first checkpoint
* the item is being committed into.
*/
if (!lv->lv_item->li_seq)
lv->lv_item->li_seq = log->l_cilp->xc_ctx->sequence;
}
/*
* Format log item into a flat buffers
*
* For delayed logging, we need to hold a formatted buffer containing all the
* changes on the log item. This enables us to relog the item in memory and
* write it out asynchronously without needing to relock the object that was
* modified at the time it gets written into the iclog.
*
* This function takes the prepared log vectors attached to each log item, and
* formats the changes into the log vector buffer. The buffer it uses is
* dependent on the current state of the vector in the CIL - the shadow lv is
* guaranteed to be large enough for the current modification, but we will only
* use that if we can't reuse the existing lv. If we can't reuse the existing
* lv, then simple swap it out for the shadow lv. We don't free it - that is
* done lazily either by th enext modification or the freeing of the log item.
*
* We don't set up region headers during this process; we simply copy the
* regions into the flat buffer. We can do this because we still have to do a
* formatting step to write the regions into the iclog buffer. Writing the
* ophdrs during the iclog write means that we can support splitting large
* regions across iclog boundares without needing a change in the format of the
* item/region encapsulation.
*
* Hence what we need to do now is change the rewrite the vector array to point
* to the copied region inside the buffer we just allocated. This allows us to
* format the regions into the iclog as though they are being formatted
* directly out of the objects themselves.
*/
static void
xlog_cil_insert_format_items(
struct xlog *log,
struct xfs_trans *tp,
int *diff_len,
int *diff_iovecs)
{
struct xfs_log_item *lip;
/* Bail out if we didn't find a log item. */
if (list_empty(&tp->t_items)) {
ASSERT(0);
return;
}
list_for_each_entry(lip, &tp->t_items, li_trans) {
struct xfs_log_vec *lv;
struct xfs_log_vec *old_lv = NULL;
struct xfs_log_vec *shadow;
bool ordered = false;
/* Skip items which aren't dirty in this transaction. */
if (!test_bit(XFS_LI_DIRTY, &lip->li_flags))
continue;
/*
* The formatting size information is already attached to
* the shadow lv on the log item.
*/
shadow = lip->li_lv_shadow;
if (shadow->lv_buf_len == XFS_LOG_VEC_ORDERED)
ordered = true;
/* Skip items that do not have any vectors for writing */
if (!shadow->lv_niovecs && !ordered)
continue;
/* compare to existing item size */
old_lv = lip->li_lv;
if (lip->li_lv && shadow->lv_size <= lip->li_lv->lv_size) {
/* same or smaller, optimise common overwrite case */
lv = lip->li_lv;
lv->lv_next = NULL;
if (ordered)
goto insert;
/*
* set the item up as though it is a new insertion so
* that the space reservation accounting is correct.
*/
*diff_iovecs -= lv->lv_niovecs;
*diff_len -= lv->lv_bytes;
/* Ensure the lv is set up according to ->iop_size */
lv->lv_niovecs = shadow->lv_niovecs;
/* reset the lv buffer information for new formatting */
lv->lv_buf_len = 0;
lv->lv_bytes = 0;
lv->lv_buf = (char *)lv +
xlog_cil_iovec_space(lv->lv_niovecs);
} else {
/* switch to shadow buffer! */
lv = shadow;
lv->lv_item = lip;
if (ordered) {
/* track as an ordered logvec */
ASSERT(lip->li_lv == NULL);
goto insert;
}
}
ASSERT(IS_ALIGNED((unsigned long)lv->lv_buf, sizeof(uint64_t)));
lip->li_ops->iop_format(lip, lv);
insert:
xfs_cil_prepare_item(log, lv, old_lv, diff_len, diff_iovecs);
}
}
/*
* Insert the log items into the CIL and calculate the difference in space
* consumed by the item. Add the space to the checkpoint ticket and calculate
* if the change requires additional log metadata. If it does, take that space
* as well. Remove the amount of space we added to the checkpoint ticket from
* the current transaction ticket so that the accounting works out correctly.
*/
static void
xlog_cil_insert_items(
struct xlog *log,
struct xfs_trans *tp)
{
struct xfs_cil *cil = log->l_cilp;
struct xfs_cil_ctx *ctx = cil->xc_ctx;
struct xfs_log_item *lip;
int len = 0;
int diff_iovecs = 0;
int iclog_space;
int iovhdr_res = 0, split_res = 0, ctx_res = 0;
ASSERT(tp);
/*
* We can do this safely because the context can't checkpoint until we
* are done so it doesn't matter exactly how we update the CIL.
*/
xlog_cil_insert_format_items(log, tp, &len, &diff_iovecs);
spin_lock(&cil->xc_cil_lock);
/* account for space used by new iovec headers */
iovhdr_res = diff_iovecs * sizeof(xlog_op_header_t);
len += iovhdr_res;
ctx->nvecs += diff_iovecs;
/* attach the transaction to the CIL if it has any busy extents */
if (!list_empty(&tp->t_busy))
list_splice_init(&tp->t_busy, &ctx->busy_extents);
/*
* Now transfer enough transaction reservation to the context ticket
* for the checkpoint. The context ticket is special - the unit
* reservation has to grow as well as the current reservation as we
* steal from tickets so we can correctly determine the space used
* during the transaction commit.
*/
if (ctx->ticket->t_curr_res == 0) {
ctx_res = ctx->ticket->t_unit_res;
ctx->ticket->t_curr_res = ctx_res;
tp->t_ticket->t_curr_res -= ctx_res;
}
/* do we need space for more log record headers? */
iclog_space = log->l_iclog_size - log->l_iclog_hsize;
if (len > 0 && (ctx->space_used / iclog_space !=
(ctx->space_used + len) / iclog_space)) {
split_res = (len + iclog_space - 1) / iclog_space;
/* need to take into account split region headers, too */
split_res *= log->l_iclog_hsize + sizeof(struct xlog_op_header);
ctx->ticket->t_unit_res += split_res;
ctx->ticket->t_curr_res += split_res;
tp->t_ticket->t_curr_res -= split_res;
ASSERT(tp->t_ticket->t_curr_res >= len);
}
tp->t_ticket->t_curr_res -= len;
ctx->space_used += len;
/*
* If we've overrun the reservation, dump the tx details before we move
* the log items. Shutdown is imminent...
*/
if (WARN_ON(tp->t_ticket->t_curr_res < 0)) {
xfs_warn(log->l_mp, "Transaction log reservation overrun:");
xfs_warn(log->l_mp,
" log items: %d bytes (iov hdrs: %d bytes)",
len, iovhdr_res);
xfs_warn(log->l_mp, " split region headers: %d bytes",
split_res);
xfs_warn(log->l_mp, " ctx ticket: %d bytes", ctx_res);
xlog_print_trans(tp);
}
/*
* Now (re-)position everything modified at the tail of the CIL.
* We do this here so we only need to take the CIL lock once during
* the transaction commit.
*/
list_for_each_entry(lip, &tp->t_items, li_trans) {
/* Skip items which aren't dirty in this transaction. */
if (!test_bit(XFS_LI_DIRTY, &lip->li_flags))
continue;
/*
* Only move the item if it isn't already at the tail. This is
* to prevent a transient list_empty() state when reinserting
* an item that is already the only item in the CIL.
*/
if (!list_is_last(&lip->li_cil, &cil->xc_cil))
list_move_tail(&lip->li_cil, &cil->xc_cil);
}
spin_unlock(&cil->xc_cil_lock);
if (tp->t_ticket->t_curr_res < 0)
xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
}
static void
xlog_cil_free_logvec(
struct xfs_log_vec *log_vector)
{
struct xfs_log_vec *lv;
for (lv = log_vector; lv; ) {
struct xfs_log_vec *next = lv->lv_next;
kmem_free(lv);
lv = next;
}
}
static void
xlog_discard_endio_work(
struct work_struct *work)
{
struct xfs_cil_ctx *ctx =
container_of(work, struct xfs_cil_ctx, discard_endio_work);
struct xfs_mount *mp = ctx->cil->xc_log->l_mp;
xfs_extent_busy_clear(mp, &ctx->busy_extents, false);
kmem_free(ctx);
}
/*
* Queue up the actual completion to a thread to avoid IRQ-safe locking for
* pagb_lock. Note that we need a unbounded workqueue, otherwise we might
* get the execution delayed up to 30 seconds for weird reasons.
*/
static void
xlog_discard_endio(
struct bio *bio)
{
struct xfs_cil_ctx *ctx = bio->bi_private;
INIT_WORK(&ctx->discard_endio_work, xlog_discard_endio_work);
queue_work(xfs_discard_wq, &ctx->discard_endio_work);
bio_put(bio);
}
static void
xlog_discard_busy_extents(
struct xfs_mount *mp,
struct xfs_cil_ctx *ctx)
{
struct list_head *list = &ctx->busy_extents;
struct xfs_extent_busy *busyp;
struct bio *bio = NULL;
struct blk_plug plug;
int error = 0;
ASSERT(mp->m_flags & XFS_MOUNT_DISCARD);
blk_start_plug(&plug);
list_for_each_entry(busyp, list, list) {
trace_xfs_discard_extent(mp, busyp->agno, busyp->bno,
busyp->length);
error = __blkdev_issue_discard(mp->m_ddev_targp->bt_bdev,
XFS_AGB_TO_DADDR(mp, busyp->agno, busyp->bno),
XFS_FSB_TO_BB(mp, busyp->length),
GFP_NOFS, 0, &bio);
if (error && error != -EOPNOTSUPP) {
xfs_info(mp,
"discard failed for extent [0x%llx,%u], error %d",
(unsigned long long)busyp->bno,
busyp->length,
error);
break;
}
}
if (bio) {
bio->bi_private = ctx;
bio->bi_end_io = xlog_discard_endio;
submit_bio(bio);
} else {
xlog_discard_endio_work(&ctx->discard_endio_work);
}
blk_finish_plug(&plug);
}
/*
* Mark all items committed and clear busy extents. We free the log vector
* chains in a separate pass so that we unpin the log items as quickly as
* possible.
*/
static void
xlog_cil_committed(
struct xfs_cil_ctx *ctx)
{
struct xfs_mount *mp = ctx->cil->xc_log->l_mp;
bool abort = XLOG_FORCED_SHUTDOWN(ctx->cil->xc_log);
/*
* If the I/O failed, we're aborting the commit and already shutdown.
* Wake any commit waiters before aborting the log items so we don't
* block async log pushers on callbacks. Async log pushers explicitly do
* not wait on log force completion because they may be holding locks
* required to unpin items.
*/
if (abort) {
spin_lock(&ctx->cil->xc_push_lock);
wake_up_all(&ctx->cil->xc_commit_wait);
spin_unlock(&ctx->cil->xc_push_lock);
}
xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
ctx->start_lsn, abort);
xfs_extent_busy_sort(&ctx->busy_extents);
xfs_extent_busy_clear(mp, &ctx->busy_extents,
(mp->m_flags & XFS_MOUNT_DISCARD) && !abort);
spin_lock(&ctx->cil->xc_push_lock);
list_del(&ctx->committing);
spin_unlock(&ctx->cil->xc_push_lock);
xlog_cil_free_logvec(ctx->lv_chain);
if (!list_empty(&ctx->busy_extents))
xlog_discard_busy_extents(mp, ctx);
else
kmem_free(ctx);
}
void
xlog_cil_process_committed(
struct list_head *list)
{
struct xfs_cil_ctx *ctx;
while ((ctx = list_first_entry_or_null(list,
struct xfs_cil_ctx, iclog_entry))) {
list_del(&ctx->iclog_entry);
xlog_cil_committed(ctx);
}
}
/*
* Push the Committed Item List to the log.
*
* If the current sequence is the same as xc_push_seq we need to do a flush. If
* xc_push_seq is less than the current sequence, then it has already been
* flushed and we don't need to do anything - the caller will wait for it to
* complete if necessary.
*
* xc_push_seq is checked unlocked against the sequence number for a match.
* Hence we can allow log forces to run racily and not issue pushes for the
* same sequence twice. If we get a race between multiple pushes for the same
* sequence they will block on the first one and then abort, hence avoiding
* needless pushes.
*/
static void
xlog_cil_push_work(
struct work_struct *work)
{
struct xfs_cil *cil =
container_of(work, struct xfs_cil, xc_push_work);
struct xlog *log = cil->xc_log;
struct xfs_log_vec *lv;
struct xfs_cil_ctx *ctx;
struct xfs_cil_ctx *new_ctx;
struct xlog_in_core *commit_iclog;
struct xlog_ticket *tic;
int num_iovecs;
int error = 0;
struct xfs_trans_header thdr;
struct xfs_log_iovec lhdr;
struct xfs_log_vec lvhdr = { NULL };
xfs_lsn_t preflush_tail_lsn;
xfs_lsn_t commit_lsn;
xfs_csn_t push_seq;
struct bio bio;
DECLARE_COMPLETION_ONSTACK(bdev_flush);
new_ctx = kmem_zalloc(sizeof(*new_ctx), KM_NOFS);
new_ctx->ticket = xlog_cil_ticket_alloc(log);
down_write(&cil->xc_ctx_lock);
ctx = cil->xc_ctx;
spin_lock(&cil->xc_push_lock);
push_seq = cil->xc_push_seq;
ASSERT(push_seq <= ctx->sequence);
/*
* As we are about to switch to a new, empty CIL context, we no longer
* need to throttle tasks on CIL space overruns. Wake any waiters that
* the hard push throttle may have caught so they can start committing
* to the new context. The ctx->xc_push_lock provides the serialisation
* necessary for safely using the lockless waitqueue_active() check in
* this context.
*/
if (waitqueue_active(&cil->xc_push_wait))
wake_up_all(&cil->xc_push_wait);
/*
* Check if we've anything to push. If there is nothing, then we don't
* move on to a new sequence number and so we have to be able to push
* this sequence again later.
*/
if (list_empty(&cil->xc_cil)) {
cil->xc_push_seq = 0;
spin_unlock(&cil->xc_push_lock);
goto out_skip;
}
/* check for a previously pushed sequence */
if (push_seq < cil->xc_ctx->sequence) {
spin_unlock(&cil->xc_push_lock);
goto out_skip;
}
/*
* We are now going to push this context, so add it to the committing
* list before we do anything else. This ensures that anyone waiting on
* this push can easily detect the difference between a "push in
* progress" and "CIL is empty, nothing to do".
*
* IOWs, a wait loop can now check for:
* the current sequence not being found on the committing list;
* an empty CIL; and
* an unchanged sequence number
* to detect a push that had nothing to do and therefore does not need
* waiting on. If the CIL is not empty, we get put on the committing
* list before emptying the CIL and bumping the sequence number. Hence
* an empty CIL and an unchanged sequence number means we jumped out
* above after doing nothing.
*
* Hence the waiter will either find the commit sequence on the
* committing list or the sequence number will be unchanged and the CIL
* still dirty. In that latter case, the push has not yet started, and
* so the waiter will have to continue trying to check the CIL
* committing list until it is found. In extreme cases of delay, the
* sequence may fully commit between the attempts the wait makes to wait
* on the commit sequence.
*/
list_add(&ctx->committing, &cil->xc_committing);
spin_unlock(&cil->xc_push_lock);
/*
* The CIL is stable at this point - nothing new will be added to it
* because we hold the flush lock exclusively. Hence we can now issue
* a cache flush to ensure all the completed metadata in the journal we
* are about to overwrite is on stable storage.
*
* Because we are issuing this cache flush before we've written the
* tail lsn to the iclog, we can have metadata IO completions move the
* tail forwards between the completion of this flush and the iclog
* being written. In this case, we need to re-issue the cache flush
* before the iclog write. To detect whether the log tail moves, sample
* the tail LSN *before* we issue the flush.
*/
preflush_tail_lsn = atomic64_read(&log->l_tail_lsn);
xfs_flush_bdev_async(&bio, log->l_mp->m_ddev_targp->bt_bdev,
&bdev_flush);
/*
* Pull all the log vectors off the items in the CIL, and remove the
* items from the CIL. We don't need the CIL lock here because it's only
* needed on the transaction commit side which is currently locked out
* by the flush lock.
*/
lv = NULL;
num_iovecs = 0;
while (!list_empty(&cil->xc_cil)) {
struct xfs_log_item *item;
item = list_first_entry(&cil->xc_cil,
struct xfs_log_item, li_cil);
list_del_init(&item->li_cil);
if (!ctx->lv_chain)
ctx->lv_chain = item->li_lv;
else
lv->lv_next = item->li_lv;
lv = item->li_lv;
item->li_lv = NULL;
num_iovecs += lv->lv_niovecs;
}
/*
* initialise the new context and attach it to the CIL. Then attach
* the current context to the CIL committing list so it can be found
* during log forces to extract the commit lsn of the sequence that
* needs to be forced.
*/
INIT_LIST_HEAD(&new_ctx->committing);
INIT_LIST_HEAD(&new_ctx->busy_extents);
new_ctx->sequence = ctx->sequence + 1;
new_ctx->cil = cil;
cil->xc_ctx = new_ctx;
/*
* The switch is now done, so we can drop the context lock and move out
* of a shared context. We can't just go straight to the commit record,
* though - we need to synchronise with previous and future commits so
* that the commit records are correctly ordered in the log to ensure
* that we process items during log IO completion in the correct order.
*
* For example, if we get an EFI in one checkpoint and the EFD in the
* next (e.g. due to log forces), we do not want the checkpoint with
* the EFD to be committed before the checkpoint with the EFI. Hence
* we must strictly order the commit records of the checkpoints so
* that: a) the checkpoint callbacks are attached to the iclogs in the
* correct order; and b) the checkpoints are replayed in correct order
* in log recovery.
*
* Hence we need to add this context to the committing context list so
* that higher sequences will wait for us to write out a commit record
* before they do.
*
* xfs_log_force_seq requires us to mirror the new sequence into the cil
* structure atomically with the addition of this sequence to the
* committing list. This also ensures that we can do unlocked checks
* against the current sequence in log forces without risking
* deferencing a freed context pointer.
*/
spin_lock(&cil->xc_push_lock);
cil->xc_current_sequence = new_ctx->sequence;
spin_unlock(&cil->xc_push_lock);
up_write(&cil->xc_ctx_lock);
/*
* Build a checkpoint transaction header and write it to the log to
* begin the transaction. We need to account for the space used by the
* transaction header here as it is not accounted for in xlog_write().
*
* The LSN we need to pass to the log items on transaction commit is
* the LSN reported by the first log vector write. If we use the commit
* record lsn then we can move the tail beyond the grant write head.
*/
tic = ctx->ticket;
thdr.th_magic = XFS_TRANS_HEADER_MAGIC;
thdr.th_type = XFS_TRANS_CHECKPOINT;
thdr.th_tid = tic->t_tid;
thdr.th_num_items = num_iovecs;
lhdr.i_addr = &thdr;
lhdr.i_len = sizeof(xfs_trans_header_t);
lhdr.i_type = XLOG_REG_TYPE_TRANSHDR;
tic->t_curr_res -= lhdr.i_len + sizeof(xlog_op_header_t);
lvhdr.lv_niovecs = 1;
lvhdr.lv_iovecp = &lhdr;
lvhdr.lv_next = ctx->lv_chain;
/*
* Before we format and submit the first iclog, we have to ensure that
* the metadata writeback ordering cache flush is complete.
*/
wait_for_completion(&bdev_flush);
error = xlog_write(log, &lvhdr, tic, &ctx->start_lsn, NULL,
XLOG_START_TRANS);
if (error)
goto out_abort_free_ticket;
/*
* now that we've written the checkpoint into the log, strictly
* order the commit records so replay will get them in the right order.
*/
restart:
spin_lock(&cil->xc_push_lock);
list_for_each_entry(new_ctx, &cil->xc_committing, committing) {
/*
* Avoid getting stuck in this loop because we were woken by the
* shutdown, but then went back to sleep once already in the
* shutdown state.
*/
if (XLOG_FORCED_SHUTDOWN(log)) {
spin_unlock(&cil->xc_push_lock);
goto out_abort_free_ticket;
}
/*
* Higher sequences will wait for this one so skip them.
* Don't wait for our own sequence, either.
*/
if (new_ctx->sequence >= ctx->sequence)
continue;
if (!new_ctx->commit_lsn) {
/*
* It is still being pushed! Wait for the push to
* complete, then start again from the beginning.
*/
xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
goto restart;
}
}
spin_unlock(&cil->xc_push_lock);
error = xlog_commit_record(log, tic, &commit_iclog, &commit_lsn);
if (error)
goto out_abort_free_ticket;
xfs_log_ticket_ungrant(log, tic);
/*
* Once we attach the ctx to the iclog, a shutdown can process the
* iclog, run the callbacks and free the ctx. The only thing preventing
* this potential UAF situation here is that we are holding the
* icloglock. Hence we cannot access the ctx once we have attached the
* callbacks and dropped the icloglock.
*/
spin_lock(&log->l_icloglock);
if (commit_iclog->ic_state == XLOG_STATE_IOERROR) {
spin_unlock(&log->l_icloglock);
goto out_abort;
}
ASSERT_ALWAYS(commit_iclog->ic_state == XLOG_STATE_ACTIVE ||
commit_iclog->ic_state == XLOG_STATE_WANT_SYNC);
list_add_tail(&ctx->iclog_entry, &commit_iclog->ic_callbacks);
/*
* now the checkpoint commit is complete and we've attached the
* callbacks to the iclog we can assign the commit LSN to the context
* and wake up anyone who is waiting for the commit to complete.
*/
spin_lock(&cil->xc_push_lock);
ctx->commit_lsn = commit_lsn;
wake_up_all(&cil->xc_commit_wait);
spin_unlock(&cil->xc_push_lock);
/*
* If the checkpoint spans multiple iclogs, wait for all previous iclogs
* to complete before we submit the commit_iclog. We can't use state
* checks for this - ACTIVE can be either a past completed iclog or a
* future iclog being filled, while WANT_SYNC through SYNC_DONE can be a
* past or future iclog awaiting IO or ordered IO completion to be run.
* In the latter case, if it's a future iclog and we wait on it, the we
* will hang because it won't get processed through to ic_force_wait
* wakeup until this commit_iclog is written to disk. Hence we use the
* iclog header lsn and compare it to the commit lsn to determine if we
* need to wait on iclogs or not.
*
* NOTE: It is not safe to reference the ctx after this check as we drop
* the icloglock if we have to wait for completion of other iclogs.
*/
if (ctx->start_lsn != commit_lsn) {
xfs_lsn_t plsn;
plsn = be64_to_cpu(commit_iclog->ic_prev->ic_header.h_lsn);
if (plsn && XFS_LSN_CMP(plsn, commit_lsn) < 0) {
/*
* Waiting on ic_force_wait orders the completion of
* iclogs older than ic_prev. Hence we only need to wait
* on the most recent older iclog here.
*/
xlog_wait_on_iclog(commit_iclog->ic_prev);
spin_lock(&log->l_icloglock);
}
/*
* We need to issue a pre-flush so that the ordering for this
* checkpoint is correctly preserved down to stable storage.
*/
commit_iclog->ic_flags |= XLOG_ICL_NEED_FLUSH;
}
/*
* The commit iclog must be written to stable storage to guarantee
* journal IO vs metadata writeback IO is correctly ordered on stable
* storage.
*/
commit_iclog->ic_flags |= XLOG_ICL_NEED_FUA;
xlog_state_release_iclog(log, commit_iclog, preflush_tail_lsn);
spin_unlock(&log->l_icloglock);
return;
out_skip:
up_write(&cil->xc_ctx_lock);
xfs_log_ticket_put(new_ctx->ticket);
kmem_free(new_ctx);
return;
out_abort_free_ticket:
xfs_log_ticket_ungrant(log, tic);
out_abort:
ASSERT(XLOG_FORCED_SHUTDOWN(log));
xlog_cil_committed(ctx);
}
/*
* We need to push CIL every so often so we don't cache more than we can fit in
* the log. The limit really is that a checkpoint can't be more than half the
* log (the current checkpoint is not allowed to overwrite the previous
* checkpoint), but commit latency and memory usage limit this to a smaller
* size.
*/
static void
xlog_cil_push_background(
struct xlog *log) __releases(cil->xc_ctx_lock)
{
struct xfs_cil *cil = log->l_cilp;
/*
* The cil won't be empty because we are called while holding the
* context lock so whatever we added to the CIL will still be there
*/
ASSERT(!list_empty(&cil->xc_cil));
/*
* Don't do a background push if we haven't used up all the
* space available yet.
*/
if (cil->xc_ctx->space_used < XLOG_CIL_SPACE_LIMIT(log)) {
up_read(&cil->xc_ctx_lock);
return;
}
spin_lock(&cil->xc_push_lock);
if (cil->xc_push_seq < cil->xc_current_sequence) {
cil->xc_push_seq = cil->xc_current_sequence;