linux-ext4 - [PATCH 1/3] quota: Prevent memory allocation recursion while holding dq

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Date:   Sun,  5 Jun 2022 15:38:13 +0100
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     Jan Kara <jack@...e.com>
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>, tytso@....edu,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH 1/3] quota: Prevent memory allocation recursion while holding dq_lock

As described in commit 02117b8ae9c0 ("f2fs: Set GF_NOFS in
read_cache_page_gfp while doing f2fs_quota_read"), we must not enter
filesystem reclaim while holding the dq_lock.  Prevent this more generally
by using memalloc_nofs_save() while holding the lock.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 fs/quota/dquot.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index a74aef99bd3d..cdb22d6d7488 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -425,9 +425,11 @@ EXPORT_SYMBOL(mark_info_dirty);
 int dquot_acquire(struct dquot *dquot)
 {
 	int ret = 0, ret2 = 0;
+	unsigned int memalloc;
 	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
 
 	mutex_lock(&dquot->dq_lock);
+	memalloc = memalloc_nofs_save();
 	if (!test_bit(DQ_READ_B, &dquot->dq_flags)) {
 		ret = dqopt->ops[dquot->dq_id.type]->read_dqblk(dquot);
 		if (ret < 0)
@@ -458,6 +460,7 @@ int dquot_acquire(struct dquot *dquot)
 	smp_mb__before_atomic();
 	set_bit(DQ_ACTIVE_B, &dquot->dq_flags);
 out_iolock:
+	memalloc_nofs_restore(memalloc);
 	mutex_unlock(&dquot->dq_lock);
 	return ret;
 }
@@ -469,9 +472,11 @@ EXPORT_SYMBOL(dquot_acquire);
 int dquot_commit(struct dquot *dquot)
 {
 	int ret = 0;
+	unsigned int memalloc;
 	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
 
 	mutex_lock(&dquot->dq_lock);
+	memalloc = memalloc_nofs_save();
 	if (!clear_dquot_dirty(dquot))
 		goto out_lock;
 	/* Inactive dquot can be only if there was error during read/init
@@ -481,6 +486,7 @@ int dquot_commit(struct dquot *dquot)
 	else
 		ret = -EIO;
 out_lock:
+	memalloc_nofs_restore(memalloc);
 	mutex_unlock(&dquot->dq_lock);
 	return ret;
 }
@@ -492,9 +498,11 @@ EXPORT_SYMBOL(dquot_commit);
 int dquot_release(struct dquot *dquot)
 {
 	int ret = 0, ret2 = 0;
+	unsigned int memalloc;
 	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
 
 	mutex_lock(&dquot->dq_lock);
+	memalloc = memalloc_nofs_save();
 	/* Check whether we are not racing with some other dqget() */
 	if (dquot_is_busy(dquot))
 		goto out_dqlock;
@@ -510,6 +518,7 @@ int dquot_release(struct dquot *dquot)
 	}
 	clear_bit(DQ_ACTIVE_B, &dquot->dq_flags);
 out_dqlock:
+	memalloc_nofs_restore(memalloc);
 	mutex_unlock(&dquot->dq_lock);
 	return ret;
 }
-- 
2.35.1