linux-kernel - [PATCH] fscrypt: fix lockdep warning

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Date:   Tue,  4 Oct 2022 18:13:26 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     "Theodore Y . Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH] fscrypt: fix lockdep warning

fscrypt_initialize() shouldn't allocate memory without GFP_NOFS.

The problem seems to go back to 2015
commit 57e5055b0a5e ("f2fs crypto: add f2fs encryption facilities")
but I have never heard of any complaints, hence not CC'ing stable.

  ======================================================
  WARNING: possible circular locking dependency detected
  6.0.0-lockdep #1 Not tainted
  ------------------------------------------------------
  kswapd0/77 is trying to acquire lock:
  71ffff808b254a18 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0x76c/0x8dc

  but task is already holding lock:
  ffffffea26533310 (fs_reclaim){+.+.}-{0:0}, at: 0x1

  which lock already depends on the new lock.

  <snipped>

  other info that might help us debug this:

  Chain exists of:
    jbd2_handle --> fscrypt_init_mutex --> fs_reclaim

   Possible unsafe locking scenario:

         CPU0                    CPU1
         ----                    ----
    lock(fs_reclaim);
                                 lock(fscrypt_init_mutex);
                                 lock(fs_reclaim);
    lock(jbd2_handle);

   *** DEADLOCK ***

  3 locks held by kswapd0/77:
   #0: ffffffea26533310 (fs_reclaim){+.+.}-{0:0}, at: 0x1
   #1: ffffffea26529220 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x54/0x464
   #2: 6dffff808abe90e8 (&type->s_umount_key#47){++++}-{3:3}, at: trylock_super+0x2c/0x8c

  <snipped>

Signed-off-by: Yu Zhao <yuzhao@...gle.com>
---
 fs/crypto/crypto.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index e78be66bbf01..e10fc30142a6 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -316,6 +316,7 @@ EXPORT_SYMBOL(fscrypt_decrypt_block_inplace);
 int fscrypt_initialize(unsigned int cop_flags)
 {
 	int err = 0;
+	unsigned int flags;
 
 	/* No need to allocate a bounce page pool if this FS won't use it. */
 	if (cop_flags & FS_CFLG_OWN_PAGES)
@@ -326,8 +327,10 @@ int fscrypt_initialize(unsigned int cop_flags)
 		goto out_unlock;
 
 	err = -ENOMEM;
+	flags = memalloc_nofs_save();
 	fscrypt_bounce_page_pool =
 		mempool_create_page_pool(num_prealloc_crypto_pages, 0);
+	memalloc_nofs_restore(flags);
 	if (!fscrypt_bounce_page_pool)
 		goto out_unlock;
 
-- 
2.38.0.rc1.362.ged0d419d3c-goog