linux-ext4 - [PATCH] ext4: Drop the call to ext4_error() from ext4_get_group

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Date:   Wed, 14 Jun 2023 12:02:55 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        syzbot+4acc7d910e617b360859@...kaller.appspotmail.com
Subject: [PATCH] ext4: Drop the call to ext4_error() from ext4_get_group_info()

A recent patch added a call to ext4_error() which is problematic since
some callers of the ext4_get_group_info() function may be holding a
spinlock, whereas ext4_error() must never be called in atomic context.

This triggered a report from Syzbot: "BUG: sleeping function called from
invalid context in ext4_update_super" (see the link below).

Therefore, drop the call to ext4_error() from ext4_get_group_info(). In
the meantime use eight characters tabs instead of nine characters ones.

Reported-by: syzbot+4acc7d910e617b360859@...kaller.appspotmail.com
Closes: https://lore.kernel.org/all/00000000000070575805fdc6cdb2@google.com/
Fixes: 5354b2af3406 ("ext4: allow ext4_get_group_info() to fail")
Suggested-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---
 fs/ext4/balloc.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index c1edde817be8..e8da678a0103 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -324,17 +324,15 @@ static ext4_fsblk_t ext4_valid_block_bitmap_padding(struct super_block *sb,
 struct ext4_group_info *ext4_get_group_info(struct super_block *sb,
 					    ext4_group_t group)
 {
-	 struct ext4_group_info **grp_info;
-	 long indexv, indexh;
-
-	 if (unlikely(group >= EXT4_SB(sb)->s_groups_count)) {
-		 ext4_error(sb, "invalid group %u", group);
-		 return NULL;
-	 }
-	 indexv = group >> (EXT4_DESC_PER_BLOCK_BITS(sb));
-	 indexh = group & ((EXT4_DESC_PER_BLOCK(sb)) - 1);
-	 grp_info = sbi_array_rcu_deref(EXT4_SB(sb), s_group_info, indexv);
-	 return grp_info[indexh];
+	struct ext4_group_info **grp_info;
+	long indexv, indexh;
+
+	if (unlikely(group >= EXT4_SB(sb)->s_groups_count))
+		return NULL;
+	indexv = group >> (EXT4_DESC_PER_BLOCK_BITS(sb));
+	indexh = group & ((EXT4_DESC_PER_BLOCK(sb)) - 1);
+	grp_info = sbi_array_rcu_deref(EXT4_SB(sb), s_group_info, indexv);
+	return grp_info[indexh];
 }
 
 /*
-- 
2.41.0