Messages in this thread | | | Subject | Re: [PATCH v2 1/2] fuse: Fix possible deadlock when writing back dirty pages | From | Baolin Wang <> | Date | Mon, 12 Apr 2021 21:23:50 +0800 |
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Hi Miklos,
在 2021/3/27 14:36, Baolin Wang 写道: > We can meet below deadlock scenario when writing back dirty pages, and > writing files at the same time. The deadlock scenario can be reproduced > by: > > - A writeback worker thread A is trying to write a bunch of dirty pages by > fuse_writepages(), and the fuse_writepages() will lock one page (named page 1), > add it into rb_tree with setting writeback flag, and unlock this page 1, > then try to lock next page (named page 2). > > - But at the same time a file writing can be triggered by another process B, > to write several pages by fuse_perform_write(), the fuse_perform_write() > will lock all required pages firstly, then wait for all writeback pages > are completed by fuse_wait_on_page_writeback(). > > - Now the process B can already lock page 1 and page 2, and wait for page 1 > waritehack is completed (page 1 is under writeback set by process A). But > process A can not complete the writeback of page 1, since it is still > waiting for locking page 2, which was locked by process B already. > > A deadlock is occurred. > > To fix this issue, we should make sure each page writeback is completed > after lock the page in fuse_fill_write_pages() separately, and then write > them together when all pages are stable. > > [1450578.772896] INFO: task kworker/u259:6:119885 blocked for more than 120 seconds. > [1450578.796179] kworker/u259:6 D 0 119885 2 0x00000028 > [1450578.796185] Workqueue: writeback wb_workfn (flush-0:78) > [1450578.796188] Call trace: > [1450578.798804] __switch_to+0xd8/0x148 > [1450578.802458] __schedule+0x280/0x6a0 > [1450578.806112] schedule+0x34/0xe8 > [1450578.809413] io_schedule+0x20/0x40 > [1450578.812977] __lock_page+0x164/0x278 > [1450578.816718] write_cache_pages+0x2b0/0x4a8 > [1450578.820986] fuse_writepages+0x84/0x100 [fuse] > [1450578.825592] do_writepages+0x58/0x108 > [1450578.829412] __writeback_single_inode+0x48/0x448 > [1450578.834217] writeback_sb_inodes+0x220/0x520 > [1450578.838647] __writeback_inodes_wb+0x50/0xe8 > [1450578.843080] wb_writeback+0x294/0x3b8 > [1450578.846906] wb_do_writeback+0x2ec/0x388 > [1450578.850992] wb_workfn+0x80/0x1e0 > [1450578.854472] process_one_work+0x1bc/0x3f0 > [1450578.858645] worker_thread+0x164/0x468 > [1450578.862559] kthread+0x108/0x138 > [1450578.865960] INFO: task doio:207752 blocked for more than 120 seconds. > [1450578.888321] doio D 0 207752 207740 0x00000000 > [1450578.888329] Call trace: > [1450578.890945] __switch_to+0xd8/0x148 > [1450578.894599] __schedule+0x280/0x6a0 > [1450578.898255] schedule+0x34/0xe8 > [1450578.901568] fuse_wait_on_page_writeback+0x8c/0xc8 [fuse] > [1450578.907128] fuse_perform_write+0x240/0x4e0 [fuse] > [1450578.912082] fuse_file_write_iter+0x1dc/0x290 [fuse] > [1450578.917207] do_iter_readv_writev+0x110/0x188 > [1450578.921724] do_iter_write+0x90/0x1c8 > [1450578.925598] vfs_writev+0x84/0xf8 > [1450578.929071] do_writev+0x70/0x110 > [1450578.932552] __arm64_sys_writev+0x24/0x30 > [1450578.936727] el0_svc_common.constprop.0+0x80/0x1f8 > [1450578.941694] el0_svc_handler+0x30/0x80 > [1450578.945606] el0_svc+0x10/0x14 > > Suggested-by: Peng Tao <tao.peng@linux.alibaba.com> > Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Do you have any comments for this patch set? Thanks.
> --- > Changes from v1: > - Use fuse_wait_on_page_writeback() instead to wait for page stable. > --- > fs/fuse/file.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 8cccecb..9a30093 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -1101,9 +1101,6 @@ static ssize_t fuse_send_write_pages(struct fuse_io_args *ia, > unsigned int offset, i; > int err; > > - for (i = 0; i < ap->num_pages; i++) > - fuse_wait_on_page_writeback(inode, ap->pages[i]->index); > - > fuse_write_args_fill(ia, ff, pos, count); > ia->write.in.flags = fuse_write_flags(iocb); > if (fm->fc->handle_killpriv_v2 && !capable(CAP_FSETID)) > @@ -1140,6 +1137,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_args_pages *ap, > unsigned int max_pages) > { > struct fuse_conn *fc = get_fuse_conn(mapping->host); > + struct inode *inode = mapping->host; > unsigned offset = pos & (PAGE_SIZE - 1); > size_t count = 0; > int err; > @@ -1166,6 +1164,8 @@ static ssize_t fuse_fill_write_pages(struct fuse_args_pages *ap, > if (!page) > break; > > + fuse_wait_on_page_writeback(inode, page->index); > + > if (mapping_writably_mapped(mapping)) > flush_dcache_page(page); > >
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