journal_remove_journal_head() can oops when trying to access journal_head
returned by bh2jh(). This is caused for example by the following race:
TASK1 TASK2
journal_commit_transaction()
...
processing t_forget list
__journal_refile_buffer(jh);
if (!jh->b_transaction) {
jbd_unlock_bh_state(bh);
journal_try_to_free_buffers()
journal_grab_journal_head(bh)
jbd_lock_bh_state(bh)
__journal_try_to_free_buffer()
journal_put_journal_head(jh)
journal_remove_journal_head(bh);
journal_put_journal_head() in TASK2 sees that b_jcount == 0 and buffer is not
part of any transaction and thus frees journal_head before TASK1 gets to doing
so. Note that even buffer_head can be released by try_to_free_buffers() after
journal_put_journal_head() which adds even larger opportunity for oops (but I
didn't see this happen in reality).
Fix the problem by making transactions hold their own journal_head reference
(in b_jcount). That way we don't have to remove journal_head explicitely via
journal_remove_journal_head() and instead just remove journal_head when
b_jcount drops to zero. The result of this is that [__]journal_refile_buffer(),
[__]journal_unfile_buffer(), and __journal_remove_checkpoint() can free
journal_head which needs modification of a few callers. Also we have to be
careful because once journal_head is removed, buffer_head might be freed as
well. So we have to get our own buffer_head reference where it matters.
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/jbd/checkpoint.c | 27 ++++++++------
fs/jbd/commit.c | 46 +++++++++++-------------
fs/jbd/journal.c | 95 ++++++++++++++++---------------------------------
fs/jbd/transaction.c | 73 +++++++++++++++++++-------------------
include/linux/jbd.h | 1 -
5 files changed, 104 insertions(+), 138 deletions(-)
- port of JBD2 commit de1b794130b130e77ffa975bb58cb843744f9ae5
v2:
- fixed data buffers handling
- this patch survived my testing so I've put it in my tree
diff --git a/fs/jbd/checkpoint.c b/fs/jbd/checkpoint.c
index dea7503..61655a3 100644
--- a/fs/jbd/checkpoint.c
+++ b/fs/jbd/checkpoint.c
@@ -96,10 +96,14 @@ static int __try_to_free_cp_buf(struct journal_head *jh)
if (jh->b_jlist == BJ_None && !buffer_locked(bh) &&
!buffer_dirty(bh) && !buffer_write_io_error(bh)) {
+ /*
+ * Get our reference so that bh cannot be freed before
+ * we unlock it
+ */
+ get_bh(bh);
JBUFFER_TRACE(jh, "remove from checkpoint list");
ret = __journal_remove_checkpoint(jh) + 1;
jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
BUFFER_TRACE(bh, "release");
__brelse(bh);
} else {
@@ -221,8 +225,8 @@ restart:
spin_lock(&journal->j_list_lock);
goto restart;
}
+ get_bh(bh);
if (buffer_locked(bh)) {
- get_bh(bh);
spin_unlock(&journal->j_list_lock);
jbd_unlock_bh_state(bh);
wait_on_buffer(bh);
@@ -241,7 +245,6 @@ restart:
*/
released = __journal_remove_checkpoint(jh);
jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
__brelse(bh);
}
@@ -305,12 +308,12 @@ static int __process_buffer(journal_t *journal, struct journal_head *jh,
ret = 1;
if (unlikely(buffer_write_io_error(bh)))
ret = -EIO;
+ get_bh(bh);
J_ASSERT_JH(jh, !buffer_jbddirty(bh));
BUFFER_TRACE(bh, "remove from checkpoint");
__journal_remove_checkpoint(jh);
spin_unlock(&journal->j_list_lock);
jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
__brelse(bh);
} else {
/*
@@ -526,9 +529,9 @@ int cleanup_journal_tail(journal_t *journal)
/*
* journal_clean_one_cp_list
*
- * Find all the written-back checkpoint buffers in the given list and release them.
+ * Find all the written-back checkpoint buffers in the given list and release
+ * them.
*
- * Called with the journal locked.
* Called with j_list_lock held.
* Returns number of bufers reaped (for debug)
*/
@@ -635,8 +638,8 @@ out:
* checkpoint lists.
*
* The function returns 1 if it frees the transaction, 0 otherwise.
+ * The function can free jh and bh.
*
- * This function is called with the journal locked.
* This function is called with j_list_lock held.
* This function is called with jbd_lock_bh_state(jh2bh(jh))
*/
@@ -655,13 +658,14 @@ int __journal_remove_checkpoint(struct journal_head *jh)
}
journal = transaction->t_journal;
+ JBUFFER_TRACE(jh, "removing from transaction");
__buffer_unlink(jh);
jh->b_cp_transaction = NULL;
+ journal_put_journal_head(jh);
if (transaction->t_checkpoint_list != NULL ||
transaction->t_checkpoint_io_list != NULL)
goto out;
- JBUFFER_TRACE(jh, "transaction has no more buffers");
/*
* There is one special case to worry about: if we have just pulled the
@@ -672,10 +676,8 @@ int __journal_remove_checkpoint(struct journal_head *jh)
* The locking here around t_state is a bit sleazy.
* See the comment at the end of journal_commit_transaction().
*/
- if (transaction->t_state != T_FINISHED) {
- JBUFFER_TRACE(jh, "belongs to running/committing transaction");
+ if (transaction->t_state != T_FINISHED)
goto out;
- }
/* OK, that was the last buffer for the transaction: we can now
safely remove this transaction from the log */
@@ -687,7 +689,6 @@ int __journal_remove_checkpoint(struct journal_head *jh)
wake_up(&journal->j_wait_logspace);
ret = 1;
out:
- JBUFFER_TRACE(jh, "exit");
return ret;
}
@@ -706,6 +707,8 @@ void __journal_insert_checkpoint(struct journal_head *jh,
J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
+ /* Get reference for checkpointing transaction */
+ journal_grab_journal_head(jh2bh(jh));
jh->b_cp_transaction = transaction;
if (!transaction->t_checkpoint_list) {
diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
index eedd201..8799207 100644
--- a/fs/jbd/commit.c
+++ b/fs/jbd/commit.c
@@ -258,10 +258,6 @@ write_out_data:
jbd_unlock_bh_state(bh);
if (locked)
unlock_buffer(bh);
- journal_remove_journal_head(bh);
- /* One for our safety reference, other for
- * journal_remove_journal_head() */
- put_bh(bh);
release_data_buffer(bh);
}
@@ -455,14 +451,9 @@ void journal_commit_transaction(journal_t *journal)
}
if (buffer_jbd(bh) && bh2jh(bh) == jh &&
jh->b_transaction == commit_transaction &&
- jh->b_jlist == BJ_Locked) {
+ jh->b_jlist == BJ_Locked)
__journal_unfile_buffer(jh);
- jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
- put_bh(bh);
- } else {
- jbd_unlock_bh_state(bh);
- }
+ jbd_unlock_bh_state(bh);
release_data_buffer(bh);
cond_resched_lock(&journal->j_list_lock);
}
@@ -807,10 +798,16 @@ restart_loop:
while (commit_transaction->t_forget) {
transaction_t *cp_transaction;
struct buffer_head *bh;
+ int try_to_free = 0;
jh = commit_transaction->t_forget;
spin_unlock(&journal->j_list_lock);
bh = jh2bh(jh);
+ /*
+ * Get a reference so that bh cannot be freed before we are
+ * done with it.
+ */
+ get_bh(bh);
jbd_lock_bh_state(bh);
J_ASSERT_JH(jh, jh->b_transaction == commit_transaction ||
jh->b_transaction == journal->j_running_transaction);
@@ -868,28 +865,27 @@ restart_loop:
__journal_insert_checkpoint(jh, commit_transaction);
if (is_journal_aborted(journal))
clear_buffer_jbddirty(bh);
- JBUFFER_TRACE(jh, "refile for checkpoint writeback");
- __journal_refile_buffer(jh);
- jbd_unlock_bh_state(bh);
} else {
J_ASSERT_BH(bh, !buffer_dirty(bh));
- /* The buffer on BJ_Forget list and not jbddirty means
+ /*
+ * The buffer on BJ_Forget list and not jbddirty means
* it has been freed by this transaction and hence it
* could not have been reallocated until this
* transaction has committed. *BUT* it could be
* reallocated once we have written all the data to
* disk and before we process the buffer on BJ_Forget
- * list. */
- JBUFFER_TRACE(jh, "refile or unfile freed buffer");
- __journal_refile_buffer(jh);
- if (!jh->b_transaction) {
- jbd_unlock_bh_state(bh);
- /* needs a brelse */
- journal_remove_journal_head(bh);
- release_buffer_page(bh);
- } else
- jbd_unlock_bh_state(bh);
+ * list.
+ */
+ if (!jh->b_next_transaction)
+ try_to_free = 1;
}
+ JBUFFER_TRACE(jh, "refile or unfile freed buffer");
+ __journal_refile_buffer(jh);
+ jbd_unlock_bh_state(bh);
+ if (try_to_free)
+ release_buffer_page(bh);
+ else
+ __brelse(bh);
cond_resched_lock(&journal->j_list_lock);
}
spin_unlock(&journal->j_list_lock);
diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index ab019ee..9fe061f 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -1803,10 +1803,9 @@ static void journal_free_journal_head(struct journal_head *jh)
* When a buffer has its BH_JBD bit set it is immune from being released by
* core kernel code, mainly via ->b_count.
*
- * A journal_head may be detached from its buffer_head when the journal_head's
- * b_transaction, b_cp_transaction and b_next_transaction pointers are NULL.
- * Various places in JBD call journal_remove_journal_head() to indicate that the
- * journal_head can be dropped if needed.
+ * A journal_head is detached from its buffer_head when the journal_head's
+ * b_jcount reaches zero. Running transaction (b_transaction) and checkpoint
+ * transaction (b_cp_transaction) hold their references to b_jcount.
*
* Various places in the kernel want to attach a journal_head to a buffer_head
* _before_ attaching the journal_head to a transaction. To protect the
@@ -1819,17 +1818,16 @@ static void journal_free_journal_head(struct journal_head *jh)
* (Attach a journal_head if needed. Increments b_jcount)
* struct journal_head *jh = journal_add_journal_head(bh);
* ...
- * jh->b_transaction = xxx;
- * journal_put_journal_head(jh);
- *
- * Now, the journal_head's b_jcount is zero, but it is safe from being released
- * because it has a non-zero b_transaction.
+ * (Get another reference for transaction)
+ * journal_grab_journal_head(bh);
+ * jh->b_transaction = xxx;
+ * (Put original reference)
+ * journal_put_journal_head(jh);
*/
/*
* Give a buffer_head a journal_head.
*
- * Doesn't need the journal lock.
* May sleep.
*/
struct journal_head *journal_add_journal_head(struct buffer_head *bh)
@@ -1893,61 +1891,29 @@ static void __journal_remove_journal_head(struct buffer_head *bh)
struct journal_head *jh = bh2jh(bh);
J_ASSERT_JH(jh, jh->b_jcount >= 0);
-
- get_bh(bh);
- if (jh->b_jcount == 0) {
- if (jh->b_transaction == NULL &&
- jh->b_next_transaction == NULL &&
- jh->b_cp_transaction == NULL) {
- J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
- J_ASSERT_BH(bh, buffer_jbd(bh));
- J_ASSERT_BH(bh, jh2bh(jh) == bh);
- BUFFER_TRACE(bh, "remove journal_head");
- if (jh->b_frozen_data) {
- printk(KERN_WARNING "%s: freeing "
- "b_frozen_data\n",
- __func__);
- jbd_free(jh->b_frozen_data, bh->b_size);
- }
- if (jh->b_committed_data) {
- printk(KERN_WARNING "%s: freeing "
- "b_committed_data\n",
- __func__);
- jbd_free(jh->b_committed_data, bh->b_size);
- }
- bh->b_private = NULL;
- jh->b_bh = NULL; /* debug, really */
- clear_buffer_jbd(bh);
- __brelse(bh);
- journal_free_journal_head(jh);
- } else {
- BUFFER_TRACE(bh, "journal_head was locked");
- }
+ J_ASSERT_JH(jh, jh->b_transaction == NULL);
+ J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
+ J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
+ J_ASSERT_JH(jh, jh->b_jlist == BJ_None);
+ J_ASSERT_BH(bh, buffer_jbd(bh));
+ J_ASSERT_BH(bh, jh2bh(jh) == bh);
+ BUFFER_TRACE(bh, "remove journal_head");
+ if (jh->b_frozen_data) {
+ printk(KERN_WARNING "%s: freeing b_frozen_data\n", __func__);
+ jbd_free(jh->b_frozen_data, bh->b_size);
}
+ if (jh->b_committed_data) {
+ printk(KERN_WARNING "%s: freeing b_committed_data\n", __func__);
+ jbd_free(jh->b_committed_data, bh->b_size);
+ }
+ bh->b_private = NULL;
+ jh->b_bh = NULL; /* debug, really */
+ clear_buffer_jbd(bh);
+ journal_free_journal_head(jh);
}
/*
- * journal_remove_journal_head(): if the buffer isn't attached to a transaction
- * and has a zero b_jcount then remove and release its journal_head. If we did
- * see that the buffer is not used by any transaction we also "logically"
- * decrement ->b_count.
- *
- * We in fact take an additional increment on ->b_count as a convenience,
- * because the caller usually wants to do additional things with the bh
- * after calling here.
- * The caller of journal_remove_journal_head() *must* run __brelse(bh) at some
- * time. Once the caller has run __brelse(), the buffer is eligible for
- * reaping by try_to_free_buffers().
- */
-void journal_remove_journal_head(struct buffer_head *bh)
-{
- jbd_lock_bh_journal_head(bh);
- __journal_remove_journal_head(bh);
- jbd_unlock_bh_journal_head(bh);
-}
-
-/*
- * Drop a reference on the passed journal_head. If it fell to zero then try to
+ * Drop a reference on the passed journal_head. If it fell to zero then
* release the journal_head from the buffer_head.
*/
void journal_put_journal_head(struct journal_head *jh)
@@ -1957,11 +1923,12 @@ void journal_put_journal_head(struct journal_head *jh)
jbd_lock_bh_journal_head(bh);
J_ASSERT_JH(jh, jh->b_jcount > 0);
--jh->b_jcount;
- if (!jh->b_jcount && !jh->b_transaction) {
+ if (!jh->b_jcount) {
__journal_remove_journal_head(bh);
+ jbd_unlock_bh_journal_head(bh);
__brelse(bh);
- }
- jbd_unlock_bh_journal_head(bh);
+ } else
+ jbd_unlock_bh_journal_head(bh);
}
/*
diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c
index dc39efd..7e59c6e 100644
--- a/fs/jbd/transaction.c
+++ b/fs/jbd/transaction.c
@@ -696,7 +696,6 @@ repeat:
if (!jh->b_transaction) {
JBUFFER_TRACE(jh, "no transaction");
J_ASSERT_JH(jh, !jh->b_next_transaction);
- jh->b_transaction = transaction;
JBUFFER_TRACE(jh, "file as BJ_Reserved");
spin_lock(&journal->j_list_lock);
__journal_file_buffer(jh, transaction, BJ_Reserved);
@@ -818,7 +817,6 @@ int journal_get_create_access(handle_t *handle, struct buffer_head *bh)
* committed and so it's safe to clear the dirty bit.
*/
clear_buffer_dirty(jh2bh(jh));
- jh->b_transaction = transaction;
/* first access by this transaction */
jh->b_modified = 0;
@@ -1069,8 +1067,9 @@ int journal_dirty_data(handle_t *handle, struct buffer_head *bh)
ret = -EIO;
goto no_journal;
}
-
- if (jh->b_transaction != NULL) {
+ /* We might have slept so buffer could be refiled now */
+ if (jh->b_transaction != NULL &&
+ jh->b_transaction != handle->h_transaction) {
JBUFFER_TRACE(jh, "unfile from commit");
__journal_temp_unlink_buffer(jh);
/* It still points to the committing
@@ -1091,8 +1090,6 @@ int journal_dirty_data(handle_t *handle, struct buffer_head *bh)
if (jh->b_jlist != BJ_SyncData && jh->b_jlist != BJ_Locked) {
JBUFFER_TRACE(jh, "not on correct data list: unfile");
J_ASSERT_JH(jh, jh->b_jlist != BJ_Shadow);
- __journal_temp_unlink_buffer(jh);
- jh->b_transaction = handle->h_transaction;
JBUFFER_TRACE(jh, "file as data");
__journal_file_buffer(jh, handle->h_transaction,
BJ_SyncData);
@@ -1300,8 +1297,6 @@ int journal_forget (handle_t *handle, struct buffer_head *bh)
__journal_file_buffer(jh, transaction, BJ_Forget);
} else {
__journal_unfile_buffer(jh);
- journal_remove_journal_head(bh);
- __brelse(bh);
if (!buffer_jbd(bh)) {
spin_unlock(&journal->j_list_lock);
jbd_unlock_bh_state(bh);
@@ -1622,19 +1617,32 @@ static void __journal_temp_unlink_buffer(struct journal_head *jh)
mark_buffer_dirty(bh); /* Expose it to the VM */
}
+/*
+ * Remove buffer from all transactions.
+ *
+ * Called with bh_state lock and j_list_lock
+ *
+ * jh and bh may be already freed when this function returns.
+ */
void __journal_unfile_buffer(struct journal_head *jh)
{
__journal_temp_unlink_buffer(jh);
jh->b_transaction = NULL;
+ journal_put_journal_head(jh);
}
void journal_unfile_buffer(journal_t *journal, struct journal_head *jh)
{
- jbd_lock_bh_state(jh2bh(jh));
+ struct buffer_head *bh = jh2bh(jh);
+
+ /* Get reference so that buffer cannot be freed before we unlock it */
+ get_bh(bh);
+ jbd_lock_bh_state(bh);
spin_lock(&journal->j_list_lock);
__journal_unfile_buffer(jh);
spin_unlock(&journal->j_list_lock);
- jbd_unlock_bh_state(jh2bh(jh));
+ jbd_unlock_bh_state(bh);
+ __brelse(bh);
}
/*
@@ -1661,16 +1669,12 @@ __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
/* A written-back ordered data buffer */
JBUFFER_TRACE(jh, "release data");
__journal_unfile_buffer(jh);
- journal_remove_journal_head(bh);
- __brelse(bh);
}
} else if (jh->b_cp_transaction != NULL && jh->b_transaction == NULL) {
/* written-back checkpointed metadata buffer */
if (jh->b_jlist == BJ_None) {
JBUFFER_TRACE(jh, "remove from checkpoint list");
__journal_remove_checkpoint(jh);
- journal_remove_journal_head(bh);
- __brelse(bh);
}
}
spin_unlock(&journal->j_list_lock);
@@ -1733,7 +1737,7 @@ int journal_try_to_free_buffers(journal_t *journal,
/*
* We take our own ref against the journal_head here to avoid
* having to add tons of locking around each instance of
- * journal_remove_journal_head() and journal_put_journal_head().
+ * journal_put_journal_head().
*/
jh = journal_grab_journal_head(bh);
if (!jh)
@@ -1770,10 +1774,9 @@ static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
int may_free = 1;
struct buffer_head *bh = jh2bh(jh);
- __journal_unfile_buffer(jh);
-
if (jh->b_cp_transaction) {
JBUFFER_TRACE(jh, "on running+cp transaction");
+ __journal_temp_unlink_buffer(jh);
/*
* We don't want to write the buffer anymore, clear the
* bit so that we don't confuse checks in
@@ -1784,8 +1787,7 @@ static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction)
may_free = 0;
} else {
JBUFFER_TRACE(jh, "on running transaction");
- journal_remove_journal_head(bh);
- __brelse(bh);
+ __journal_unfile_buffer(jh);
}
return may_free;
}
@@ -2070,6 +2072,8 @@ void __journal_file_buffer(struct journal_head *jh,
if (jh->b_transaction)
__journal_temp_unlink_buffer(jh);
+ else
+ journal_grab_journal_head(bh);
jh->b_transaction = transaction;
switch (jlist) {
@@ -2127,9 +2131,10 @@ void journal_file_buffer(struct journal_head *jh,
* already started to be used by a subsequent transaction, refile the
* buffer on that transaction's metadata list.
*
- * Called under journal->j_list_lock
- *
+ * Called under j_list_lock
* Called under jbd_lock_bh_state(jh2bh(jh))
+ *
+ * jh and bh may be already free when this function returns
*/
void __journal_refile_buffer(struct journal_head *jh)
{
@@ -2153,6 +2158,11 @@ void __journal_refile_buffer(struct journal_head *jh)
was_dirty = test_clear_buffer_jbddirty(bh);
__journal_temp_unlink_buffer(jh);
+ /*
+ * We set b_transaction here because b_next_transaction will inherit
+ * our jh reference and thus __journal_file_buffer() must not take a
+ * new one.
+ */
jh->b_transaction = jh->b_next_transaction;
jh->b_next_transaction = NULL;
if (buffer_freed(bh))
@@ -2169,30 +2179,21 @@ void __journal_refile_buffer(struct journal_head *jh)
}
/*
- * For the unlocked version of this call, also make sure that any
- * hanging journal_head is cleaned up if necessary.
- *
- * __journal_refile_buffer is usually called as part of a single locked
- * operation on a buffer_head, in which the caller is probably going to
- * be hooking the journal_head onto other lists. In that case it is up
- * to the caller to remove the journal_head if necessary. For the
- * unlocked journal_refile_buffer call, the caller isn't going to be
- * doing anything else to the buffer so we need to do the cleanup
- * ourselves to avoid a jh leak.
- *
- * *** The journal_head may be freed by this call! ***
+ * __journal_refile_buffer() with necessary locking added. We take our bh
+ * reference so that we can safely unlock bh.
+ *
+ * The jh and bh may be freed by this call.
*/
void journal_refile_buffer(journal_t *journal, struct journal_head *jh)
{
struct buffer_head *bh = jh2bh(jh);
+ /* Get reference so that buffer cannot be freed before we unlock it */
+ get_bh(bh);
jbd_lock_bh_state(bh);
spin_lock(&journal->j_list_lock);
-
__journal_refile_buffer(jh);
jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
-
spin_unlock(&journal->j_list_lock);
__brelse(bh);
}
diff --git a/include/linux/jbd.h b/include/linux/jbd.h
index e069650..e6a5e34 100644
--- a/include/linux/jbd.h
+++ b/include/linux/jbd.h
@@ -940,7 +940,6 @@ extern int journal_force_commit(journal_t *);
*/
struct journal_head *journal_add_journal_head(struct buffer_head *bh);
struct journal_head *journal_grab_journal_head(struct buffer_head *bh);
-void journal_remove_journal_head(struct buffer_head *bh);
void journal_put_journal_head(struct journal_head *jh);
/*
--
1.7.1
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
