[PATCH 5.10 v3 1/7] xfs: use current->journal_info for detecting transaction recursion

Amir Goldstein
2022-07-03T05:05:08Z

From: Dave Chinner <dchinner@redhat.com>

commit 756b1c343333a5aefcc26b0409f3fd16f72281bf upstream.

Because the iomap code using PF_MEMALLOC_NOFS to detect transaction
recursion in XFS is just wrong. Remove it from the iomap code and
replace it with XFS specific internal checks using
current->journal_info instead.

[djwong: This change also realigns the lifetime of NOFS flag changes to
match the incore transaction, instead of the inconsistent scheme we have
now.]

Fixes: 9070733b4efa ("xfs: abstract PF_FSTRANS to PF_MEMALLOC_NOFS")
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
---
fs/iomap/buffered-io.c | 7 -------
fs/xfs/libxfs/xfs_btree.c | 12 ++++++++++--
fs/xfs/xfs_aops.c | 17 +++++++++++++++--
fs/xfs/xfs_trans.c | 20 +++++---------------
fs/xfs/xfs_trans.h | 30 ++++++++++++++++++++++++++++++
5 files changed, 60 insertions(+), 26 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index dd33b31b0a82..86297f59b43e 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1460,13 +1460,6 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
PF_MEMALLOC))
goto redirty;

- /*
- * Given that we do not allow direct reclaim to call us, we should
- * never be called in a recursive filesystem reclaim context.
- */
- if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
- goto redirty;
-
/*
* Is this page beyond the end of the file?
*
diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
index 98c82f4935e1..24c7d30e41df 100644
--- a/fs/xfs/libxfs/xfs_btree.c
+++ b/fs/xfs/libxfs/xfs_btree.c
@@ -2811,7 +2811,7 @@ xfs_btree_split_worker(
struct xfs_btree_split_args *args = container_of(work,
struct xfs_btree_split_args, work);
unsigned long pflags;
- unsigned long new_pflags = PF_MEMALLOC_NOFS;
+ unsigned long new_pflags = 0;

/*
* we are in a transaction context here, but may also be doing work
@@ -2823,12 +2823,20 @@ xfs_btree_split_worker(
new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;

current_set_flags_nested(&pflags, new_pflags);
+ xfs_trans_set_context(args->cur->bc_tp);

args->result = __xfs_btree_split(args->cur, args->level, args->ptrp,
args->key, args->curp, args->stat);
- complete(args->done);

+ xfs_trans_clear_context(args->cur->bc_tp);
current_restore_flags_nested(&pflags, new_pflags);
+
+ /*
+ * Do not access args after complete() has run here. We don't own args
+ * and the owner may run and free args before we return here.
+ */
+ complete(args->done);
+
}

/*
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 4b76a32d2f16..953de843d9c3 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -62,7 +62,7 @@ xfs_setfilesize_trans_alloc(
* We hand off the transaction to the completion thread now, so
* clear the flag here.
*/
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ xfs_trans_clear_context(tp);
return 0;
}

@@ -125,7 +125,7 @@ xfs_setfilesize_ioend(
* thus we need to mark ourselves as being in a transaction manually.
* Similarly for freeze protection.
*/
- current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ xfs_trans_set_context(tp);
__sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS);

/* we abort the update if there was an IO error */
@@ -577,6 +577,12 @@ xfs_vm_writepage(
{
struct xfs_writepage_ctx wpc = { };

+ if (WARN_ON_ONCE(current->journal_info)) {
+ redirty_page_for_writepage(wbc, page);
+ unlock_page(page);
+ return 0;
+ }
+
return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops);
}

@@ -587,6 +593,13 @@ xfs_vm_writepages(
{
struct xfs_writepage_ctx wpc = { };

+ /*
+ * Writing back data in a transaction context can result in recursive
+ * transactions. This is bad, so issue a warning and get out of here.
+ */
+ if (WARN_ON_ONCE(current->journal_info))
+ return 0;
+
xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops);
}
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index c94e71f741b6..2d7deacea2cf 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -68,6 +68,7 @@ xfs_trans_free(
xfs_extent_busy_clear(tp->t_mountp, &tp->t_busy, false);

trace_xfs_trans_free(tp, _RET_IP_);
+ xfs_trans_clear_context(tp);
if (!(tp->t_flags & XFS_TRANS_NO_WRITECOUNT))
sb_end_intwrite(tp->t_mountp->m_super);
xfs_trans_free_dqinfo(tp);
@@ -119,7 +120,8 @@ xfs_trans_dup(

ntp->t_rtx_res = tp->t_rtx_res - tp->t_rtx_res_used;
tp->t_rtx_res = tp->t_rtx_res_used;
- ntp->t_pflags = tp->t_pflags;
+
+ xfs_trans_switch_context(tp, ntp);

/* move deferred ops over to the new tp */
xfs_defer_move(ntp, tp);
@@ -153,9 +155,6 @@ xfs_trans_reserve(
int error = 0;
bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;

- /* Mark this thread as being in a transaction */
- current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
-
/*
* Attempt to reserve the needed disk blocks by decrementing
* the number needed from the number available. This will
@@ -163,10 +162,8 @@ xfs_trans_reserve(
*/
if (blocks > 0) {
error = xfs_mod_fdblocks(mp, -((int64_t)blocks), rsvd);
- if (error != 0) {
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ if (error != 0)
return -ENOSPC;
- }
tp->t_blk_res += blocks;
}

@@ -240,9 +237,6 @@ xfs_trans_reserve(
xfs_mod_fdblocks(mp, (int64_t)blocks, rsvd);
tp->t_blk_res = 0;
}
-
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
-
return error;
}

@@ -266,6 +260,7 @@ xfs_trans_alloc(
tp = kmem_cache_zalloc(xfs_trans_zone, GFP_KERNEL | __GFP_NOFAIL);
if (!(flags & XFS_TRANS_NO_WRITECOUNT))
sb_start_intwrite(mp->m_super);
+ xfs_trans_set_context(tp);

/*
* Zero-reservation ("empty") transactions can't modify anything, so
@@ -878,7 +873,6 @@ __xfs_trans_commit(

xfs_log_commit_cil(mp, tp, &commit_lsn, regrant);

- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
xfs_trans_free(tp);

/*
@@ -910,7 +904,6 @@ __xfs_trans_commit(
xfs_log_ticket_ungrant(mp->m_log, tp->t_ticket);
tp->t_ticket = NULL;
}
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
xfs_trans_free_items(tp, !!error);
xfs_trans_free(tp);

@@ -970,9 +963,6 @@ xfs_trans_cancel(
tp->t_ticket = NULL;
}

- /* mark this thread as no longer being in a transaction */
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
-
xfs_trans_free_items(tp, dirty);
xfs_trans_free(tp);
}
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index 084658946cc8..075eeade4f7d 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -268,4 +268,34 @@ xfs_trans_item_relog(
return lip->li_ops->iop_relog(lip, tp);
}

+static inline void
+xfs_trans_set_context(
+ struct xfs_trans *tp)
+{
+ ASSERT(current->journal_info == NULL);
+ tp->t_pflags = memalloc_nofs_save();
+ current->journal_info = tp;
+}
+
+static inline void
+xfs_trans_clear_context(
+ struct xfs_trans *tp)
+{
+ if (current->journal_info == tp) {
+ memalloc_nofs_restore(tp->t_pflags);
+ current->journal_info = NULL;
+ }
+}
+
+static inline void
+xfs_trans_switch_context(
+ struct xfs_trans *old_tp,
+ struct xfs_trans *new_tp)
+{
+ ASSERT(current->journal_info == old_tp);
+ new_tp->t_pflags = old_tp->t_pflags;
+ old_tp->t_pflags = 0;
+ current->journal_info = new_tp;
+}
+
#endif /* __XFS_TRANS_H__ */
--
2.25.1