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SubjectRe: [PATCH v2] lockdep: Teach lockdep about memalloc_noio_save
On Wed, Mar 01, 2017 at 09:59:00AM +0200, Nikolay Borisov wrote:
> Commit 21caf2fc1931 ("mm: teach mm by current context info to not do I/O
> during memory allocation") added the memalloc_noio_(save|restore) functions
> to enable people to modify the MM behavior by disbaling I/O during memory
> allocation. This prevents allocation paths recursing back into the filesystem
> without explicitly changing the flags for every allocation site. Yet, lockdep
> not being aware of that is prone to showing false positives. Fix this
> by teaching it that the presence of PF_MEMALLOC_NOIO flag mean we are not
> going to issue any I/O

I'm not up to date on the specific, but GFP_IO is separate from GFP_FS.

And MEMALLOC_NOIO only clears GFP_IO but leaves GFP_FS set.

Therefore I think your change is wrong, but I might have overlooked a
detail. Added original authors to Cc to clarify.


> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
> kernel/locking/lockdep.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
>
> Turned out there was another place where RELCAIM_FS was being set, fix it
> by using the memalloc_noio_flags when setting ->lockdep_reclaim_gfp flags.
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 9812e5dd409e..87cf9910e66f 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -2866,7 +2866,8 @@ static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags)
> return;
>
> /* this guy won't enter reclaim */
> - if ((curr->flags & PF_MEMALLOC) && !(gfp_mask & __GFP_NOMEMALLOC))
> + if (((curr->flags & PF_MEMALLOC) && !(gfp_mask & __GFP_NOMEMALLOC)) ||
> + curr->flags & PF_MEMALLOC_NOIO)
> return;
>
> /* We're only interested __GFP_FS allocations for now */
> @@ -3852,7 +3853,7 @@ EXPORT_SYMBOL_GPL(lock_unpin_lock);
>
> void lockdep_set_current_reclaim_state(gfp_t gfp_mask)
> {
> - current->lockdep_reclaim_gfp = gfp_mask;
> + current->lockdep_reclaim_gfp = memalloc_noio_flags(gfp_mask);
> }
>
> void lockdep_clear_current_reclaim_state(void)
> --
> 2.7.4
>

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