From: Michal Hocko Date: Fri, 3 Feb 2017 21:13:26 +0000 (-0800) Subject: fs: break out of iomap_file_buffered_write on fatal signals X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=d1908f52557b3230fbd63c0429f3b4b748bf2b6d;p=linux-beck.git fs: break out of iomap_file_buffered_write on fatal signals 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 Reported-by: Tetsuo Handa Reviewed-by: Christoph Hellwig Cc: Al Viro Cc: [4.8+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/dax.c b/fs/dax.c index 3af2da5e64ce..c45598b912e1 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1031,6 +1031,11 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data, struct blk_dax_ctl dax = { 0 }; ssize_t map_len; + if (fatal_signal_pending(current)) { + ret = -EINTR; + break; + } + dax.sector = dax_iomap_sector(iomap, pos); dax.size = (length + offset + PAGE_SIZE - 1) & PAGE_MASK; map_len = dax_map_atomic(iomap->bdev, &dax); diff --git a/fs/iomap.c b/fs/iomap.c index 354a123f170e..a51cb4c07d4d 100644 --- a/fs/iomap.c +++ b/fs/iomap.c @@ -114,6 +114,9 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags, 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;