Commit 27ba5b67 authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o
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jbd2: avoid infinite transaction commit loop 



Commit 9f356e5a ("jbd2: Account descriptor blocks into
t_outstanding_credits") started to account descriptor blocks into
transactions outstanding credits. However it didn't appropriately
decrease the maximum amount of credits available to userspace. Thus if
the filesystem requests a transaction smaller than
j_max_transaction_buffers but large enough that when descriptor blocks
are added the size exceeds j_max_transaction_buffers, we confuse
add_transaction_credits() into thinking previous handles have grown the
transaction too much and enter infinite journal commit loop in
start_this_handle() -> add_transaction_credits() trying to create
transaction with enough credits available.

Fix the problem by properly accounting for transaction space reserved
for descriptor blocks when verifying requested transaction handle size.

CC: stable@vger.kernel.org
Fixes: 9f356e5a ("jbd2: Account descriptor blocks into t_outstanding_credits")
Reported-by: default avatarAlexander Coffin <alex.coffin@maticrobots.com>
Link: https://lore.kernel.org/all/CA+hUFcuGs04JHZ_WzA1zGN57+ehL2qmHOt5a7RMpo+rv6Vyxtw@mail.gmail.com


Signed-off-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarZhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20240624170127.3253-3-jack@suse.cz


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent e3a00a23

fs/jbd2/transaction.c

+14 −7
Original line number Diff line number Diff line
@@ -191,6 +191,13 @@ static void sub_reserved_credits(journal_t *journal, int blocks) 
	wake_up(&journal->j_wait_reserved);

}



/* Maximum number of blocks for user transaction payload */

static int jbd2_max_user_trans_buffers(journal_t *journal)

{

	return journal->j_max_transaction_buffers -

				journal->j_transaction_overhead_buffers;

}



/*

 * Wait until we can add credits for handle to the running transaction.  Called

 * with j_state_lock held for reading. Returns 0 if handle joined the running
@@ -240,12 +247,12 @@ __must_hold(&journal->j_state_lock) 
		 * big to fit this handle? Wait until reserved credits are freed.

		 */

		if (atomic_read(&journal->j_reserved_credits) + total >

		    journal->j_max_transaction_buffers) {

		    jbd2_max_user_trans_buffers(journal)) {

			read_unlock(&journal->j_state_lock);

			jbd2_might_wait_for_commit(journal);

			wait_event(journal->j_wait_reserved,

				   atomic_read(&journal->j_reserved_credits) + total <=

				   journal->j_max_transaction_buffers);

				   jbd2_max_user_trans_buffers(journal));

			__acquire(&journal->j_state_lock); /* fake out sparse */

			return 1;

		}
@@ -285,14 +292,14 @@ __must_hold(&journal->j_state_lock) 


	needed = atomic_add_return(rsv_blocks, &journal->j_reserved_credits);

	/* We allow at most half of a transaction to be reserved */

	if (needed > journal->j_max_transaction_buffers / 2) {

	if (needed > jbd2_max_user_trans_buffers(journal) / 2) {

		sub_reserved_credits(journal, rsv_blocks);

		atomic_sub(total, &t->t_outstanding_credits);

		read_unlock(&journal->j_state_lock);

		jbd2_might_wait_for_commit(journal);

		wait_event(journal->j_wait_reserved,

			 atomic_read(&journal->j_reserved_credits) + rsv_blocks

			 <= journal->j_max_transaction_buffers / 2);

			 <= jbd2_max_user_trans_buffers(journal) / 2);

		__acquire(&journal->j_state_lock); /* fake out sparse */

		return 1;

	}
@@ -322,12 +329,12 @@ static int start_this_handle(journal_t *journal, handle_t *handle, 
	 * size and limit the number of total credits to not exceed maximum

	 * transaction size per operation.

	 */

	if ((rsv_blocks > journal->j_max_transaction_buffers / 2) ||

	    (rsv_blocks + blocks > journal->j_max_transaction_buffers)) {

	if (rsv_blocks > jbd2_max_user_trans_buffers(journal) / 2 ||

	    rsv_blocks + blocks > jbd2_max_user_trans_buffers(journal)) {

		printk(KERN_ERR "JBD2: %s wants too many credits "

		       "credits:%d rsv_credits:%d max:%d\n",

		       current->comm, blocks, rsv_blocks,

		       journal->j_max_transaction_buffers);

		       jbd2_max_user_trans_buffers(journal));

		WARN_ON(1);

		return -ENOSPC;

	}