From 89b15332af7c0312a41e50846819ca6613b58b4c Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Sat, 30 Nov 2019 17:50:22 -0800 Subject: mm: drop mmap_sem before calling balance_dirty_pages() in write fault One of our services is observing hanging ps/top/etc under heavy write IO, and the task states show this is an mmap_sem priority inversion: A write fault is holding the mmap_sem in read-mode and waiting for (heavily cgroup-limited) IO in balance_dirty_pages(): balance_dirty_pages+0x724/0x905 balance_dirty_pages_ratelimited+0x254/0x390 fault_dirty_shared_page.isra.96+0x4a/0x90 do_wp_page+0x33e/0x400 __handle_mm_fault+0x6f0/0xfa0 handle_mm_fault+0xe4/0x200 __do_page_fault+0x22b/0x4a0 page_fault+0x45/0x50 Somebody tries to change the address space, contending for the mmap_sem in write-mode: call_rwsem_down_write_failed_killable+0x13/0x20 do_mprotect_pkey+0xa8/0x330 SyS_mprotect+0xf/0x20 do_syscall_64+0x5b/0x100 entry_SYSCALL_64_after_hwframe+0x3d/0xa2 The waiting writer locks out all subsequent readers to avoid lock starvation, and several threads can be seen hanging like this: call_rwsem_down_read_failed+0x14/0x30 proc_pid_cmdline_read+0xa0/0x480 __vfs_read+0x23/0x140 vfs_read+0x87/0x130 SyS_read+0x42/0x90 do_syscall_64+0x5b/0x100 entry_SYSCALL_64_after_hwframe+0x3d/0xa2 To fix this, do what we do for cache read faults already: drop the mmap_sem before calling into anything IO bound, in this case the balance_dirty_pages() function, and return VM_FAULT_RETRY. Link: http://lkml.kernel.org/r/20190924194238.GA29030@cmpxchg.org Signed-off-by: Johannes Weiner Reviewed-by: Matthew Wilcox (Oracle) Acked-by: Kirill A. Shutemov Cc: Josef Bacik Cc: Hillf Danton Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 21 --------------------- 1 file changed, 21 deletions(-) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index dc3b78db079b..bf6aa30be58d 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2329,27 +2329,6 @@ EXPORT_SYMBOL(generic_file_read_iter); #ifdef CONFIG_MMU #define MMAP_LOTSAMISS (100) -static struct file *maybe_unlock_mmap_for_io(struct vm_fault *vmf, - struct file *fpin) -{ - int flags = vmf->flags; - - if (fpin) - return fpin; - - /* - * FAULT_FLAG_RETRY_NOWAIT means we don't want to wait on page locks or - * anything, so we only pin the file and drop the mmap_sem if only - * FAULT_FLAG_ALLOW_RETRY is set. - */ - if ((flags & (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT)) == - FAULT_FLAG_ALLOW_RETRY) { - fpin = get_file(vmf->vma->vm_file); - up_read(&vmf->vma->vm_mm->mmap_sem); - } - return fpin; -} - /* * lock_page_maybe_drop_mmap - lock the page, possibly dropping the mmap_sem * @vmf - the vm_fault for this fault. -- cgit v1.2.3