Re: [syzbot] inconsistent lock state in kmem_cache_alloc

[Sebastian Andrzej Siewior]

On 2022-09-29 15:24:22 [+0200], Vlastimil Babka wrote:
> I'm not fully sure what this report means but I assume it's because there's
> a GFP_KERNEL kmalloc() allocation from softirq context? Should it perhaps
> use memalloc_nofs_save() at some well defined point?

my guess is
…
> > Call Trace:
> >  <IRQ>
…
> >  __fs_reclaim_acquire mm/page_alloc.c:4674 [inline]
> >  fs_reclaim_acquire+0x115/0x160 mm/page_alloc.c:4688
> >  might_alloc include/linux/sched/mm.h:271 [inline]
> >  slab_pre_alloc_hook mm/slab.h:700 [inline]
> >  slab_alloc mm/slab.c:3278 [inline]
> >  __kmem_cache_alloc_lru mm/slab.c:3471 [inline]
> >  kmem_cache_alloc+0x39/0x520 mm/slab.c:3491
> >  fanotify_alloc_fid_event fs/notify/fanotify/fanotify.c:580 [inline]
> >  fanotify_alloc_event fs/notify/fanotify/fanotify.c:813 [inline]

this sets GFP to GFP_KERNEL_ACCOUNT + (__GFP_NOFAIL ||
__GFP_RETRY_MAYFAIL) which contains GFP_KERNEL and

> >  fanotify_handle_event+0x1130/0x3f40 fs/notify/fanotify/fanotify.c:948
> >  send_to_group fs/notify/fsnotify.c:360 [inline]
> >  fsnotify+0xafb/0x1680 fs/notify/fsnotify.c:570
> >  __fsnotify_parent+0x62f/0xa60 fs/notify/fsnotify.c:230
> >  fsnotify_parent include/linux/fsnotify.h:77 [inline]
> >  fsnotify_file include/linux/fsnotify.h:99 [inline]
> >  fsnotify_access include/linux/fsnotify.h:309 [inline]
> >  __io_complete_rw_common+0x485/0x720 io_uring/rw.c:195
> >  io_complete_rw+0x1a/0x1f0 io_uring/rw.c:228
> >  iomap_dio_complete_work fs/iomap/direct-io.c:144 [inline]
> >  iomap_dio_bio_end_io+0x438/0x5e0 fs/iomap/direct-io.c:178
> >  bio_endio+0x5f9/0x780 block/bio.c:1564
> >  req_bio_endio block/blk-mq.c:695 [inline]
> >  blk_update_request+0x3fc/0x1300 block/blk-mq.c:825
> >  scsi_end_request+0x7a/0x9a0 drivers/scsi/scsi_lib.c:541
> >  scsi_io_completion+0x173/0x1f70 drivers/scsi/scsi_lib.c:971
> >  scsi_complete+0x122/0x3b0 drivers/scsi/scsi_lib.c:1438
> >  blk_complete_reqs+0xad/0xe0 block/blk-mq.c:1022
> >  __do_softirq+0x1d3/0x9c6 kernel/softirq.c:571
> >  invoke_softirq kernel/softirq.c:445 [inline]
> >  __irq_exit_rcu+0x123/0x180 kernel/softirq.c:650
> >  irq_exit_rcu+0x5/0x20 kernel/softirq.c:662
> >  common_interrupt+0xa9/0xc0 arch/x86/kernel/irq.c:240
> >  </IRQ>
…

we originate from softirq we can't use GFP_KERNEL. This also noted here:

> > BUG: sleeping function called from invalid context at include/linux/sched/mm.h:274
> > in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/1
> > preempt_count: 101, expected: 0
> > RCU nest depth: 0, expected: 0
> > INFO: lockdep is turned off.
> > Preemption disabled at:
> > [<0000000000000000>] 0x0
> > CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.0.0-rc6-syzkaller-00321-g105a36f3694e #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
> > Call Trace:
> >  <IRQ>
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
> >  __might_resched.cold+0x222/0x26b kernel/sched/core.c:9892
> >  might_alloc include/linux/sched/mm.h:274 [inline]
> >  slab_pre_alloc_hook mm/slab.h:700 [inline]
> >  slab_alloc mm/slab.c:3278 [inline]
> >  __kmem_cache_alloc_lru mm/slab.c:3471 [inline]
> >  kmem_cache_alloc+0x381/0x520 mm/slab.c:3491
> >  fanotify_alloc_fid_event fs/notify/fanotify/fanotify.c:580 [inline]
> >  fanotify_alloc_event fs/notify/fanotify/fanotify.c:813 [inline]
> >  fanotify_handle_event+0x1130/0x3f40 fs/notify/fanotify/fanotify.c:948

So either the caller needs to be put into task-context or
fanotify_alloc_event() needs something like

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index cd7d09a569fff..9f6c5813f7a93 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -710,7 +710,7 @@ static struct fanotify_event *fanotify_alloc_event(
 				__kernel_fsid_t *fsid, u32 match_mask)
 {
 	struct fanotify_event *event = NULL;
-	gfp_t gfp = GFP_KERNEL_ACCOUNT;
+	gfp_t gfp = GFP_ATOMIC | __GFP_ACCOUNT;
 	unsigned int fid_mode = FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS);
 	struct inode *id = fanotify_fid_inode(mask, data, data_type, dir,
 					      fid_mode);

Sebastian