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List:       linux-mm
Subject:    Re: [PATCH] mm, fs: Obey gfp_mapping for add_to_page_cache
From:       Andrew Morton <akpm () linux-foundation ! org>
Date:       2015-09-29 22:02:46
Message-ID: 20150929150246.286cc6013bce3eec170376aa () linux-foundation ! org
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On Fri, 25 Sep 2015 17:04:21 +0200 mhocko@kernel.org wrote:

> From: Michal Hocko <mhocko@suse.com>
> 
> 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?

> this is a rebase on top of the current mmotm
> (2015-09-22-15-28)

So I've redone the patch against current mainline.

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