Re: [PATCH] mm, fs: Obey gfp_mapping for add_to_page_cache

[Michal Hocko]

On Tue 29-09-15 15:02:46, Andrew Morton wrote:
> On Fri, 25 Sep 2015 17:04:21 +0200 mhocko@xxxxxxxxxx wrote:
> 
> > From: Michal Hocko <mhocko@xxxxxxxx>
> > 
> > 6afdb859b710 ("mm: do not ignore mapping_gfp_mask in page cache
> > allocation paths) has caught some users of hardcoded GFP_KERNEL
> > used in the page cache allocation paths. This, however, wasn't complete
> > and there were others which went unnoticed.
> > 
> > Dave Chinner has reported the following deadlock for xfs on loop device:
> > : With the recent merge of the loop device changes, I'm now seeing
> > : XFS deadlock on my single CPU, 1GB RAM VM running xfs/073.
> > :
> > : The deadlocked is as follows:
> > :
> > : kloopd1: loop_queue_read_work
> > :       xfs_file_iter_read
> > :       lock XFS inode XFS_IOLOCK_SHARED (on image file)
> > :       page cache read (GFP_KERNEL)
> > :       radix tree alloc
> > :       memory reclaim
> > :       reclaim XFS inodes
> > :       log force to unpin inodes
> > :       <wait for log IO completion>
> > :
> > : xfs-cil/loop1: <does log force IO work>
> > :       xlog_cil_push
> > :       xlog_write
> > :       <loop issuing log writes>
> > :               xlog_state_get_iclog_space()
> > :               <blocks due to all log buffers under write io>
> > :               <waits for IO completion>
> > :
> > : kloopd1: loop_queue_write_work
> > :       xfs_file_write_iter
> > :       lock XFS inode XFS_IOLOCK_EXCL (on image file)
> > :       <wait for inode to be unlocked>
> > :
> > : i.e. the kloopd, with it's split read and write work queues, has
> > : introduced a dependency through memory reclaim. i.e. that writes
> > : need to be able to progress for reads make progress.
> > :
> > : The problem, fundamentally, is that mpage_readpages() does a
> > : GFP_KERNEL allocation, rather than paying attention to the inode's
> > : mapping gfp mask, which is set to GFP_NOFS.
> > :
> > : The didn't used to happen, because the loop device used to issue
> > : reads through the splice path and that does:
> > :
> > :       error = add_to_page_cache_lru(page, mapping, index,
> > :                       GFP_KERNEL & mapping_gfp_mask(mapping));
> > 
> > This has changed by aa4d86163e4 (block: loop: switch to VFS ITER_BVEC).
> 
> xfs-on-loop deadlocks since April would appear to warrant a -stable
> backport, yes?

Yeah, stable 4.1+

> > this is a rebase on top of the current mmotm
> > (2015-09-22-15-28)
> 
> So I've redone the patch against current mainline.

Thanks!

-- 
Michal Hocko
SUSE Labs
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