6.6-stable review patch. If anyone has any objections, please let me know.
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From: Dave Chinner dchinner@redhat.com
commit f2e812c1522dab847912309b00abcc762dd696da upstream.
syzbot reported an ext4 panic during a page fault where found a journal handle when it didn't expect to find one. The structure it tripped over had a value of 'TRAN' in the first entry in the structure, and that indicates it tripped over a struct xfs_trans instead of a jbd2 handle.
The reason for this is that the page fault was taken during a copy-out to a user buffer from an xfs bulkstat operation. XFS uses an "empty" transaction context for bulkstat to do automated metadata buffer cleanup, and so the transaction context is valid across the copyout of the bulkstat info into the user buffer.
We are using empty transaction contexts like this in XFS to reduce the risk of failing to release objects we reference during the operation, especially during error handling. Hence we really need to ensure that we can take page faults from these contexts without leaving landmines for the code processing the page fault to trip over.
However, this same behaviour could happen from any other filesystem that triggers a page fault or any other exception that is handled on-stack from within a task context that has current->journal_info set. Having a page fault from some other filesystem bounce into XFS where we have to run a transaction isn't a bug at all, but the usage of current->journal_info means that this could result corruption of the outer task's journal_info structure.
The problem is purely that we now have two different contexts that now think they own current->journal_info. IOWs, no filesystem can allow page faults or on-stack exceptions while current->journal_info is set by the filesystem because the exception processing might use current->journal_info itself.
If we end up with nested XFS transactions whilst holding an empty transaction, then it isn't an issue as the outer transaction does not hold a log reservation. If we ignore the current->journal_info usage, then the only problem that might occur is a deadlock if the exception tries to take the same locks the upper context holds. That, however, is not a problem that setting current->journal_info would solve, so it's largely an irrelevant concern here.
IOWs, we really only use current->journal_info for a warning check in xfs_vm_writepages() to ensure we aren't doing writeback from a transaction context. Writeback might need to do allocation, so it can need to run transactions itself. Hence it's a debug check to warn us that we've done something silly, and largely it is not all that useful.
So let's just remove all the use of current->journal_info in XFS and get rid of all the potential issues from nested contexts where current->journal_info might get misused by another filesystem context.
Reported-by: syzbot+cdee56dbcdf0096ef605@syzkaller.appspotmail.com Signed-off-by: Dave Chinner dchinner@redhat.com Reviewed-by: "Darrick J. Wong" djwong@kernel.org Reviewed-by: Mark Tinguely mark.tinguely@oracle.com Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Chandan Babu R chandanbabu@kernel.org Signed-off-by: Catherine Hoang catherine.hoang@oracle.com Acked-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/xfs/scrub/common.c | 4 +--- fs/xfs/xfs_aops.c | 7 ------- fs/xfs/xfs_icache.c | 8 +++++--- fs/xfs/xfs_trans.h | 9 +-------- 4 files changed, 7 insertions(+), 21 deletions(-)
--- a/fs/xfs/scrub/common.c +++ b/fs/xfs/scrub/common.c @@ -978,9 +978,7 @@ xchk_irele( struct xfs_scrub *sc, struct xfs_inode *ip) { - if (current->journal_info != NULL) { - ASSERT(current->journal_info == sc->tp); - + if (sc->tp) { /* * If we are in a transaction, we /cannot/ drop the inode * ourselves, because the VFS will trigger writeback, which --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -502,13 +502,6 @@ xfs_vm_writepages( { struct xfs_writepage_ctx wpc = { };
- /* - * Writing back data in a transaction context can result in recursive - * transactions. This is bad, so issue a warning and get out of here. - */ - if (WARN_ON_ONCE(current->journal_info)) - return 0; - xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED); return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops); } --- a/fs/xfs/xfs_icache.c +++ b/fs/xfs/xfs_icache.c @@ -2031,8 +2031,10 @@ xfs_inodegc_want_queue_work( * - Memory shrinkers queued the inactivation worker and it hasn't finished. * - The queue depth exceeds the maximum allowable percpu backlog. * - * Note: If the current thread is running a transaction, we don't ever want to - * wait for other transactions because that could introduce a deadlock. + * Note: If we are in a NOFS context here (e.g. current thread is running a + * transaction) the we don't want to block here as inodegc progress may require + * filesystem resources we hold to make progress and that could result in a + * deadlock. Hence we skip out of here if we are in a scoped NOFS context. */ static inline bool xfs_inodegc_want_flush_work( @@ -2040,7 +2042,7 @@ xfs_inodegc_want_flush_work( unsigned int items, unsigned int shrinker_hits) { - if (current->journal_info) + if (current->flags & PF_MEMALLOC_NOFS) return false;
if (shrinker_hits > 0) --- a/fs/xfs/xfs_trans.h +++ b/fs/xfs/xfs_trans.h @@ -277,19 +277,14 @@ static inline void xfs_trans_set_context( struct xfs_trans *tp) { - ASSERT(current->journal_info == NULL); tp->t_pflags = memalloc_nofs_save(); - current->journal_info = tp; }
static inline void xfs_trans_clear_context( struct xfs_trans *tp) { - if (current->journal_info == tp) { - memalloc_nofs_restore(tp->t_pflags); - current->journal_info = NULL; - } + memalloc_nofs_restore(tp->t_pflags); }
static inline void @@ -297,10 +292,8 @@ xfs_trans_switch_context( struct xfs_trans *old_tp, struct xfs_trans *new_tp) { - ASSERT(current->journal_info == old_tp); new_tp->t_pflags = old_tp->t_pflags; old_tp->t_pflags = 0; - current->journal_info = new_tp; }
#endif /* __XFS_TRANS_H__ */