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    Subject[PATCH 4.9 65/66] fs: break out of iomap_file_buffered_write on fatal signals
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Michal Hocko <mhocko@suse.com>

    commit d1908f52557b3230fbd63c0429f3b4b748bf2b6d upstream.

    Tetsuo has noticed that an OOM stress test which performs large write
    requests can cause the full memory reserves depletion. He has tracked
    this down to the following path

    __alloc_pages_nodemask+0x436/0x4d0
    alloc_pages_current+0x97/0x1b0
    __page_cache_alloc+0x15d/0x1a0 mm/filemap.c:728
    pagecache_get_page+0x5a/0x2b0 mm/filemap.c:1331
    grab_cache_page_write_begin+0x23/0x40 mm/filemap.c:2773
    iomap_write_begin+0x50/0xd0 fs/iomap.c:118
    iomap_write_actor+0xb5/0x1a0 fs/iomap.c:190
    ? iomap_write_end+0x80/0x80 fs/iomap.c:150
    iomap_apply+0xb3/0x130 fs/iomap.c:79
    iomap_file_buffered_write+0x68/0xa0 fs/iomap.c:243
    ? iomap_write_end+0x80/0x80
    xfs_file_buffered_aio_write+0x132/0x390 [xfs]
    ? remove_wait_queue+0x59/0x60
    xfs_file_write_iter+0x90/0x130 [xfs]
    __vfs_write+0xe5/0x140
    vfs_write+0xc7/0x1f0
    ? syscall_trace_enter+0x1d0/0x380
    SyS_write+0x58/0xc0
    do_syscall_64+0x6c/0x200
    entry_SYSCALL64_slow_path+0x25/0x25

    the oom victim has access to all memory reserves to make a forward
    progress to exit easier. But iomap_file_buffered_write and other
    callers of iomap_apply loop to complete the full request. We need to
    check for fatal signals and back off with a short write instead.

    As the iomap_apply delegates all the work down to the actor we have to
    hook into those. All callers that work with the page cache are calling
    iomap_write_begin so we will check for signals there. dax_iomap_actor
    has to handle the situation explicitly because it copies data to the
    userspace directly. Other callers like iomap_page_mkwrite work on a
    single page or iomap_fiemap_actor do not allocate memory based on the
    given len.

    Fixes: 68a9f5e7007c ("xfs: implement iomap based buffered write path")
    Link: http://lkml.kernel.org/r/20170201092706.9966-2-mhocko@kernel.org
    Signed-off-by: Michal Hocko <mhocko@suse.com>
    Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/dax.c | 5 +++++
    fs/iomap.c | 3 +++
    2 files changed, 8 insertions(+)

    --- a/fs/dax.c
    +++ b/fs/dax.c
    @@ -1270,6 +1270,11 @@ iomap_dax_actor(struct inode *inode, lof
    struct blk_dax_ctl dax = { 0 };
    ssize_t map_len;

    + if (fatal_signal_pending(current)) {
    + ret = -EINTR;
    + break;
    + }
    +
    dax.sector = iomap->blkno +
    (((pos & PAGE_MASK) - iomap->offset) >> 9);
    dax.size = (length + offset + PAGE_SIZE - 1) & PAGE_MASK;
    --- a/fs/iomap.c
    +++ b/fs/iomap.c
    @@ -113,6 +113,9 @@ iomap_write_begin(struct inode *inode, l

    BUG_ON(pos + len > iomap->offset + iomap->length);

    + if (fatal_signal_pending(current))
    + return -EINTR;
    +
    page = grab_cache_page_write_begin(inode->i_mapping, index, flags);
    if (!page)
    return -ENOMEM;

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