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mm: drop mmap_sem before calling balance_dirty_pages() in write fault
[ Upstream commit 89b15332af
]
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 <hannes@cmpxchg.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
parent
943cd69efa
commit
173fa52f7f
3 changed files with 50 additions and 34 deletions
21
mm/filemap.c
21
mm/filemap.c
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@ -2329,27 +2329,6 @@ EXPORT_SYMBOL(generic_file_read_iter);
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#ifdef CONFIG_MMU
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#define MMAP_LOTSAMISS (100)
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static struct file *maybe_unlock_mmap_for_io(struct vm_fault *vmf,
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struct file *fpin)
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{
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int flags = vmf->flags;
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if (fpin)
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return fpin;
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/*
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* FAULT_FLAG_RETRY_NOWAIT means we don't want to wait on page locks or
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* anything, so we only pin the file and drop the mmap_sem if only
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* FAULT_FLAG_ALLOW_RETRY is set.
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*/
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if ((flags & (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT)) ==
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FAULT_FLAG_ALLOW_RETRY) {
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fpin = get_file(vmf->vma->vm_file);
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up_read(&vmf->vma->vm_mm->mmap_sem);
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}
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return fpin;
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}
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/*
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* lock_page_maybe_drop_mmap - lock the page, possibly dropping the mmap_sem
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* @vmf - the vm_fault for this fault.
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@ -362,6 +362,27 @@ vma_address(struct page *page, struct vm_area_struct *vma)
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return max(start, vma->vm_start);
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}
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static inline struct file *maybe_unlock_mmap_for_io(struct vm_fault *vmf,
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struct file *fpin)
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{
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int flags = vmf->flags;
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if (fpin)
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return fpin;
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/*
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* FAULT_FLAG_RETRY_NOWAIT means we don't want to wait on page locks or
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* anything, so we only pin the file and drop the mmap_sem if only
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* FAULT_FLAG_ALLOW_RETRY is set.
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*/
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if ((flags & (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT)) ==
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FAULT_FLAG_ALLOW_RETRY) {
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fpin = get_file(vmf->vma->vm_file);
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up_read(&vmf->vma->vm_mm->mmap_sem);
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}
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return fpin;
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}
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#else /* !CONFIG_MMU */
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static inline void clear_page_mlock(struct page *page) { }
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static inline void mlock_vma_page(struct page *page) { }
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42
mm/memory.c
42
mm/memory.c
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@ -2227,10 +2227,11 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
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*
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* The function expects the page to be locked and unlocks it.
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*/
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static void fault_dirty_shared_page(struct vm_area_struct *vma,
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struct page *page)
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static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
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{
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struct vm_area_struct *vma = vmf->vma;
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struct address_space *mapping;
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struct page *page = vmf->page;
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bool dirtied;
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bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;
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@ -2245,16 +2246,30 @@ static void fault_dirty_shared_page(struct vm_area_struct *vma,
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mapping = page_rmapping(page);
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unlock_page(page);
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if ((dirtied || page_mkwrite) && mapping) {
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/*
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* Some device drivers do not set page.mapping
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* but still dirty their pages
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*/
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balance_dirty_pages_ratelimited(mapping);
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}
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if (!page_mkwrite)
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file_update_time(vma->vm_file);
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/*
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* Throttle page dirtying rate down to writeback speed.
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*
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* mapping may be NULL here because some device drivers do not
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* set page.mapping but still dirty their pages
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*
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* Drop the mmap_sem before waiting on IO, if we can. The file
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* is pinning the mapping, as per above.
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*/
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if ((dirtied || page_mkwrite) && mapping) {
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struct file *fpin;
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fpin = maybe_unlock_mmap_for_io(vmf, NULL);
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balance_dirty_pages_ratelimited(mapping);
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if (fpin) {
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fput(fpin);
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return VM_FAULT_RETRY;
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}
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}
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return 0;
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}
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/*
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@ -2497,6 +2512,7 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf)
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__releases(vmf->ptl)
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{
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struct vm_area_struct *vma = vmf->vma;
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vm_fault_t ret = VM_FAULT_WRITE;
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get_page(vmf->page);
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@ -2520,10 +2536,10 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf)
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wp_page_reuse(vmf);
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lock_page(vmf->page);
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}
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fault_dirty_shared_page(vma, vmf->page);
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ret |= fault_dirty_shared_page(vmf);
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put_page(vmf->page);
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return VM_FAULT_WRITE;
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return ret;
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}
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/*
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@ -3567,7 +3583,7 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
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return ret;
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}
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fault_dirty_shared_page(vma, vmf->page);
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ret |= fault_dirty_shared_page(vmf);
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return ret;
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}
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