| Message ID | 20230106115603.2624644-1-chengzhihao1@huawei.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] jbd2: Fix data missing when reusing bh which is ready to be checkpointed | expand |
On Fri 06-01-23 19:56:03, Zhihao Cheng wrote: > Following process will make data lost and could lead to a filesystem > corrupted problem: > > 1. jh(bh) is inserted into T1->t_checkpoint_list, bh is dirty, and > jh->b_transaction = NULL > 2. T1 is added into journal->j_checkpoint_transactions. > 3. Get bh prepare to write while doing checkpoing: > PA PB > do_get_write_access jbd2_log_do_checkpoint > spin_lock(&jh->b_state_lock) > if (buffer_dirty(bh)) > clear_buffer_dirty(bh) // clear buffer dirty > set_buffer_jbddirty(bh) > transaction = > journal->j_checkpoint_transactions > jh = transaction->t_checkpoint_list > if (!buffer_dirty(bh)) > __jbd2_journal_remove_checkpoint(jh) > // bh won't be flushed > jbd2_cleanup_journal_tail > __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved) > 4. Aborting journal/Power-cut before writing latest bh on journal area. > > In this way we get a corrupted filesystem with bh's data lost. > > Fix it by moving the clearing of buffer_dirty bit just before the call > to __jbd2_journal_file_buffer(), both bit clearing and jh->b_transaction > assignment are under journal->j_list_lock locked, so that > jbd2_log_do_checkpoint() will wait until jh's new transaction fininshed > even bh is currently not dirty. And journal_shrink_one_cp_list() won't > remove jh from checkpoint list if the buffer head is reused in > do_get_write_access(). > > Cc: <stable@kernel.org> > Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com> > Signed-off-by: zhanchengbin <zhanchengbin1@huawei.com> > Suggested-by: Jan Kara <jack@suse.cz> Thanks for the patch! It looks good, some suggestions for making it a bit more tidy below: > diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c > index 6a404ac1c178..06a5e7961ef2 100644 > --- a/fs/jbd2/transaction.c > +++ b/fs/jbd2/transaction.c > @@ -1010,36 +1010,37 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, > * ie. locked but not dirty) or tune2fs (which may actually have > * the buffer dirtied, ugh.) */ > > - if (buffer_dirty(bh)) { > + if (buffer_dirty(bh) && jh->b_transaction) { > /* > * First question: is this buffer already part of the current > * transaction or the existing committing transaction? > */ > - if (jh->b_transaction) { > - J_ASSERT_JH(jh, > - jh->b_transaction == transaction || > - jh->b_transaction == > - journal->j_committing_transaction); > - if (jh->b_next_transaction) > - J_ASSERT_JH(jh, jh->b_next_transaction == > - transaction); > - warn_dirty_buffer(bh); > - } > + J_ASSERT_JH(jh, jh->b_transaction == transaction || > + jh->b_transaction == journal->j_committing_transaction); > + if (jh->b_next_transaction) > + J_ASSERT_JH(jh, jh->b_next_transaction == transaction); > + warn_dirty_buffer(bh); > /* > - * In any case we need to clean the dirty flag and we must > - * do it under the buffer lock to be sure we don't race > - * with running write-out. > + * We need to clean the dirty flag and we must do it under the > + * buffer lock to be sure we don't race with running write-out. > */ > JBUFFER_TRACE(jh, "Journalling dirty buffer"); > clear_buffer_dirty(bh); > + /* > + * Setting jbddirty after clearing buffer dirty is necessary. > + * Function jbd2_journal_restart() could keep buffer on > + * BJ_Reserved list until the transaction committing, then the > + * buffer won't be dirtied by jbd2_journal_refile_buffer() > + * after committing, the buffer couldn't fall on disk even > + * last checkpoint finished, which may corrupt filesystem. > + */ > set_buffer_jbddirty(bh); > } So I think the sequence: if (buffer_dirty(bh)) { warn_dirty_buffer(bh); JBUFFER_TRACE(jh, "Journalling dirty buffer"); clear_buffer_dirty(bh); set_buffer_jbddirty(bh); } can be moved into the branch if (jh->b_transaction == transaction || jh->b_next_transaction == transaction) { below. That way you can drop the assertions as well because they happen later in do_get_write_access() again anyway. Also I don't quite understand the new comment you have added. Do you mean we need to not only clear BH_Dirty bit but also set BH_JBDdirty as dirtying (through jbd2_journal_dirty_metadata()) does not have to follow after do_get_write_access()? Otherwise the patch looks good. Honza > > - unlock_buffer(bh); > - > error = -EROFS; > if (is_handle_aborted(handle)) { > spin_unlock(&jh->b_state_lock); > + unlock_buffer(bh); > goto out; > } > error = 0; > @@ -1049,8 +1050,10 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, > * b_next_transaction points to it > */ > if (jh->b_transaction == transaction || > - jh->b_next_transaction == transaction) > + jh->b_next_transaction == transaction) { > + unlock_buffer(bh); > goto done; > + } > > /* > * this is the first time this transaction is touching this buffer, > @@ -1074,10 +1077,24 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, > */ > smp_wmb(); > spin_lock(&journal->j_list_lock); > + if (test_clear_buffer_dirty(bh)) { > + /* > + * Execute buffer dirty clearing and jh->b_transaction > + * assignment under journal->j_list_lock locked to > + * prevent bh being removed from checkpoint list if > + * the buffer is in an intermediate state (not dirty > + * and jh->b_transaction is NULL). > + */ > + JBUFFER_TRACE(jh, "Journalling dirty buffer"); > + set_buffer_jbddirty(bh); > + } > __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved); > spin_unlock(&journal->j_list_lock); > + unlock_buffer(bh); > goto done; > } > + unlock_buffer(bh); > + > /* > * If there is already a copy-out version of this buffer, then we don't > * need to make another one > -- > 2.31.1 >
在 2023/1/6 22:22, Jan Kara 写道: Hi Jan, thanks for reviewing.Some discussions below: >> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c >> index 6a404ac1c178..06a5e7961ef2 100644 >> --- a/fs/jbd2/transaction.c >> +++ b/fs/jbd2/transaction.c >> @@ -1010,36 +1010,37 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, >> * ie. locked but not dirty) or tune2fs (which may actually have >> * the buffer dirtied, ugh.) */ >> >> - if (buffer_dirty(bh)) { >> + if (buffer_dirty(bh) && jh->b_transaction) { >> /* >> * First question: is this buffer already part of the current >> * transaction or the existing committing transaction? >> */ >> - if (jh->b_transaction) { >> - J_ASSERT_JH(jh, >> - jh->b_transaction == transaction || >> - jh->b_transaction == >> - journal->j_committing_transaction); >> - if (jh->b_next_transaction) >> - J_ASSERT_JH(jh, jh->b_next_transaction == >> - transaction); >> - warn_dirty_buffer(bh); >> - } >> + J_ASSERT_JH(jh, jh->b_transaction == transaction || >> + jh->b_transaction == journal->j_committing_transaction); >> + if (jh->b_next_transaction) >> + J_ASSERT_JH(jh, jh->b_next_transaction == transaction); >> + warn_dirty_buffer(bh); >> /* >> - * In any case we need to clean the dirty flag and we must >> - * do it under the buffer lock to be sure we don't race >> - * with running write-out. >> + * We need to clean the dirty flag and we must do it under the >> + * buffer lock to be sure we don't race with running write-out. >> */ >> JBUFFER_TRACE(jh, "Journalling dirty buffer"); >> clear_buffer_dirty(bh); >> + /* >> + * Setting jbddirty after clearing buffer dirty is necessary. >> + * Function jbd2_journal_restart() could keep buffer on >> + * BJ_Reserved list until the transaction committing, then the >> + * buffer won't be dirtied by jbd2_journal_refile_buffer() >> + * after committing, the buffer couldn't fall on disk even >> + * last checkpoint finished, which may corrupt filesystem. >> + */ >> set_buffer_jbddirty(bh); >> } > > So I think the sequence: > > if (buffer_dirty(bh)) { > warn_dirty_buffer(bh); > JBUFFER_TRACE(jh, "Journalling dirty buffer"); > clear_buffer_dirty(bh); > set_buffer_jbddirty(bh); > } > > can be moved into the branch > > if (jh->b_transaction == transaction || > jh->b_next_transaction == transaction) { > > below. That way you can drop the assertions as well because they happen > later in do_get_write_access() again anyway. 1. If we move the squence: if (buffer_dirty(bh)) { warn_dirty_buffer(bh); JBUFFER_TRACE(jh, "Journalling dirty buffer"); clear_buffer_dirty(bh); set_buffer_jbddirty(bh); } into the branch if (jh->b_transaction == transaction || jh->b_next_transaction == transaction) { , then we have a new situation(jh->b_transaction == journal->j_committing_transaction) to clear buffer dirty, so we need to add an else-branch like(based on v2 patch): --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -1092,6 +1092,10 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, spin_unlock(&journal->j_list_lock); unlock_buffer(bh); goto done; + } else if (test_clear_buffer_dirty(bh)) { + warn_dirty_buffer(bh); + JBUFFER_TRACE(jh, "Journalling dirty buffer"); + set_buffer_jbddirty(bh); } unlock_buffer(bh); I think we'd better not to move the sequence? 2. I agree that the assertions in branch 'if (jh->b_transaction)' are redundant, I will remove them in v3. Thanks for pointing that. > Also I don't quite understand the new comment you have added. Do you mean > we need to not only clear BH_Dirty bit but also set BH_JBDdirty as dirtying > (through jbd2_journal_dirty_metadata()) does not have to follow after > do_get_write_access()? > Yes. I think one reason we have non-empty commit_transaction->t_reserved_list is that: jbd2_journal_restart() could let jh attach to transaction_1 and dirty jh in transaction_2. buffer is dirty after trans_0 committed do_get_write_access() => jh->trans = old_handle->trans_1, clear buffer dirty & set jbddirty, BJ_Reserved jbd2_journal_restart() => stop old_handle && may jbd2_log_start_commit && start new_handle with trans_2 jbd2_journal_commit_transaction() => clear jbddirty & set buffer dirty & set jh->b_transaction = NULL do_checkpoint => buffer is fell on disk. If do_get_write_access() not mark jbddirty, buffer won't be fell on disk after checkpoint, which could corrupt filesystem. I'm not sure whether we have the above path in realworld. I guess it exists in theory according to the comments: /* * First thing we are allowed to do is to discard any remaining * BJ_Reserved buffers. Note, it is _not_ permissible to assume * that there are no such buffers: if a large filesystem * operation like a truncate needs to split itself over multiple * transactions, then it may try to do a jbd2_journal_restart() while * there are still BJ_Reserved buffers outstanding. These must * be released cleanly from the current transaction. * * In this case, the filesystem must still reserve write access * again before modifying the buffer in the new transaction, but * we do not require it to remember exactly which old buffers it * has reserved. This is consistent with the existing behaviour * that multiple jbd2_journal_get_write_access() calls to the same * buffer are perfectly permissible. * We use journal->j_state_lock here to serialize processing of * t_reserved_list with eviction of buffers from journal_unmap_buffer(). */ while (commit_transaction->t_reserved_list) { [...]
On Sat 07-01-23 17:16:10, Zhihao Cheng wrote: > 在 2023/1/6 22:22, Jan Kara 写道: > > Hi Jan, thanks for reviewing.Some discussions below: > > > > > diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c > > > index 6a404ac1c178..06a5e7961ef2 100644 > > > --- a/fs/jbd2/transaction.c > > > +++ b/fs/jbd2/transaction.c > > > @@ -1010,36 +1010,37 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, > > > * ie. locked but not dirty) or tune2fs (which may actually have > > > * the buffer dirtied, ugh.) */ > > > - if (buffer_dirty(bh)) { > > > + if (buffer_dirty(bh) && jh->b_transaction) { > > > /* > > > * First question: is this buffer already part of the current > > > * transaction or the existing committing transaction? > > > */ > > > - if (jh->b_transaction) { > > > - J_ASSERT_JH(jh, > > > - jh->b_transaction == transaction || > > > - jh->b_transaction == > > > - journal->j_committing_transaction); > > > - if (jh->b_next_transaction) > > > - J_ASSERT_JH(jh, jh->b_next_transaction == > > > - transaction); > > > - warn_dirty_buffer(bh); > > > - } > > > + J_ASSERT_JH(jh, jh->b_transaction == transaction || > > > + jh->b_transaction == journal->j_committing_transaction); > > > + if (jh->b_next_transaction) > > > + J_ASSERT_JH(jh, jh->b_next_transaction == transaction); > > > + warn_dirty_buffer(bh); > > > /* > > > - * In any case we need to clean the dirty flag and we must > > > - * do it under the buffer lock to be sure we don't race > > > - * with running write-out. > > > + * We need to clean the dirty flag and we must do it under the > > > + * buffer lock to be sure we don't race with running write-out. > > > */ > > > JBUFFER_TRACE(jh, "Journalling dirty buffer"); > > > clear_buffer_dirty(bh); > > > + /* > > > + * Setting jbddirty after clearing buffer dirty is necessary. > > > + * Function jbd2_journal_restart() could keep buffer on > > > + * BJ_Reserved list until the transaction committing, then the > > > + * buffer won't be dirtied by jbd2_journal_refile_buffer() > > > + * after committing, the buffer couldn't fall on disk even > > > + * last checkpoint finished, which may corrupt filesystem. > > > + */ > > > set_buffer_jbddirty(bh); > > > } > > > > So I think the sequence: > > > > if (buffer_dirty(bh)) { > > warn_dirty_buffer(bh); > > JBUFFER_TRACE(jh, "Journalling dirty buffer"); > > clear_buffer_dirty(bh); > > set_buffer_jbddirty(bh); > > } > > > > can be moved into the branch > > > > if (jh->b_transaction == transaction || > > jh->b_next_transaction == transaction) { > > > > below. That way you can drop the assertions as well because they happen > > later in do_get_write_access() again anyway. > > 1. If we move the squence: > if (buffer_dirty(bh)) { > warn_dirty_buffer(bh); > JBUFFER_TRACE(jh, "Journalling dirty buffer"); > clear_buffer_dirty(bh); > set_buffer_jbddirty(bh); > } > > into the branch > > if (jh->b_transaction == transaction || > jh->b_next_transaction == transaction) { > > , then we have a new situation(jh->b_transaction == > journal->j_committing_transaction) to clear buffer dirty, so we need to add > an else-branch like(based on v2 patch): > --- a/fs/jbd2/transaction.c > +++ b/fs/jbd2/transaction.c > @@ -1092,6 +1092,10 @@ do_get_write_access(handle_t *handle, struct > journal_head *jh, > spin_unlock(&journal->j_list_lock); > unlock_buffer(bh); > goto done; > + } else if (test_clear_buffer_dirty(bh)) { > + warn_dirty_buffer(bh); > + JBUFFER_TRACE(jh, "Journalling dirty buffer"); > + set_buffer_jbddirty(bh); > } > unlock_buffer(bh); > > I think we'd better not to move the sequence? Oh, you're right. So yeah, keep this sequence where it was. > 2. I agree that the assertions in branch 'if (jh->b_transaction)' are > redundant, I will remove them in v3. Thanks for pointing that. OK, thanks! Honza
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c index 6a404ac1c178..06a5e7961ef2 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -1010,36 +1010,37 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, * ie. locked but not dirty) or tune2fs (which may actually have * the buffer dirtied, ugh.) */ - if (buffer_dirty(bh)) { + if (buffer_dirty(bh) && jh->b_transaction) { /* * First question: is this buffer already part of the current * transaction or the existing committing transaction? */ - if (jh->b_transaction) { - J_ASSERT_JH(jh, - jh->b_transaction == transaction || - jh->b_transaction == - journal->j_committing_transaction); - if (jh->b_next_transaction) - J_ASSERT_JH(jh, jh->b_next_transaction == - transaction); - warn_dirty_buffer(bh); - } + J_ASSERT_JH(jh, jh->b_transaction == transaction || + jh->b_transaction == journal->j_committing_transaction); + if (jh->b_next_transaction) + J_ASSERT_JH(jh, jh->b_next_transaction == transaction); + warn_dirty_buffer(bh); /* - * In any case we need to clean the dirty flag and we must - * do it under the buffer lock to be sure we don't race - * with running write-out. + * We need to clean the dirty flag and we must do it under the + * buffer lock to be sure we don't race with running write-out. */ JBUFFER_TRACE(jh, "Journalling dirty buffer"); clear_buffer_dirty(bh); + /* + * Setting jbddirty after clearing buffer dirty is necessary. + * Function jbd2_journal_restart() could keep buffer on + * BJ_Reserved list until the transaction committing, then the + * buffer won't be dirtied by jbd2_journal_refile_buffer() + * after committing, the buffer couldn't fall on disk even + * last checkpoint finished, which may corrupt filesystem. + */ set_buffer_jbddirty(bh); } - unlock_buffer(bh); - error = -EROFS; if (is_handle_aborted(handle)) { spin_unlock(&jh->b_state_lock); + unlock_buffer(bh); goto out; } error = 0; @@ -1049,8 +1050,10 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, * b_next_transaction points to it */ if (jh->b_transaction == transaction || - jh->b_next_transaction == transaction) + jh->b_next_transaction == transaction) { + unlock_buffer(bh); goto done; + } /* * this is the first time this transaction is touching this buffer, @@ -1074,10 +1077,24 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, */ smp_wmb(); spin_lock(&journal->j_list_lock); + if (test_clear_buffer_dirty(bh)) { + /* + * Execute buffer dirty clearing and jh->b_transaction + * assignment under journal->j_list_lock locked to + * prevent bh being removed from checkpoint list if + * the buffer is in an intermediate state (not dirty + * and jh->b_transaction is NULL). + */ + JBUFFER_TRACE(jh, "Journalling dirty buffer"); + set_buffer_jbddirty(bh); + } __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved); spin_unlock(&journal->j_list_lock); + unlock_buffer(bh); goto done; } + unlock_buffer(bh); + /* * If there is already a copy-out version of this buffer, then we don't * need to make another one
Following process will make data lost and could lead to a filesystem corrupted problem: 1. jh(bh) is inserted into T1->t_checkpoint_list, bh is dirty, and jh->b_transaction = NULL 2. T1 is added into journal->j_checkpoint_transactions. 3. Get bh prepare to write while doing checkpoing: PA PB do_get_write_access jbd2_log_do_checkpoint spin_lock(&jh->b_state_lock) if (buffer_dirty(bh)) clear_buffer_dirty(bh) // clear buffer dirty set_buffer_jbddirty(bh) transaction = journal->j_checkpoint_transactions jh = transaction->t_checkpoint_list if (!buffer_dirty(bh)) __jbd2_journal_remove_checkpoint(jh) // bh won't be flushed jbd2_cleanup_journal_tail __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved) 4. Aborting journal/Power-cut before writing latest bh on journal area. In this way we get a corrupted filesystem with bh's data lost. Fix it by moving the clearing of buffer_dirty bit just before the call to __jbd2_journal_file_buffer(), both bit clearing and jh->b_transaction assignment are under journal->j_list_lock locked, so that jbd2_log_do_checkpoint() will wait until jh's new transaction fininshed even bh is currently not dirty. And journal_shrink_one_cp_list() won't remove jh from checkpoint list if the buffer head is reused in do_get_write_access(). Cc: <stable@kernel.org> Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com> Signed-off-by: zhanchengbin <zhanchengbin1@huawei.com> Suggested-by: Jan Kara <jack@suse.cz> --- v1->v2: Adopt Jan's suggestion, move the clearing of buffer_dirty bit and __jbd2_journal_file_buffer() inside journal->j_list_lock locking area. fs/jbd2/transaction.c | 51 ++++++++++++++++++++++++++++--------------- 1 file changed, 34 insertions(+), 17 deletions(-)