tree:   https://git.kernel.org/pub/scm/linux/kernel/git/josef/btrfs-next.git 
kill-mmap-sem-v5
head:   c7a3e899803d98ae543468f0026500c651528a6c
commit: c52634339df10df75f28787f431b937de3c3c591 [9/10] mm: introduce 
filemap_page_mkwrite_nommapsem
reproduce: make htmldocs

All warnings (new ones prefixed by >>):

   WARNING: convert(1) not found, for SVG to PDF conversion install ImageMagick 
(https://www.imagemagick.org)
   include/linux/srcu.h:175: warning: Function parameter or member 'p' not 
described in 'srcu_dereference_notrace'
   include/linux/srcu.h:175: warning: Function parameter or member 'sp' not 
described in 'srcu_dereference_notrace'
   include/linux/gfp.h:1: warning: no structured comments found
>> mm/filemap.c:2882: warning: Function parameter or member 'mkwrite' not 
>> described in 'filemap_page_mkwrite_nommapsem'
   mm/filemap.c:2882: warning: Excess function parameter 'page_mkwrite_cb' 
description in 'filemap_page_mkwrite_nommapsem'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4381: warning: Function parameter or member 
'wext.ibss' not described in 'wireless_dev'
   include/net/cfg80211.h:4381: warning: Function parameter or member 
'wext.connect' not described in 'wireless_dev'
   include/net/cfg80211.h:4381: warning: Function parameter or member 
'wext.keys' not described in 'wireless_dev'
   include/net/cfg80211.h:4381: warning: Function parameter or member 'wext.ie' 
not described in 'wireless_dev'
   include/net/cfg80211.h:4381: warning: Function parameter or member 
'wext.ie_len' not described in 'wireless_dev'
   include/net/cfg80211.h:4381: warning: Function parameter or member 
'wext.bssid' not described in 'wireless_dev'
   include/net/cfg80211.h:4381: warning: Function parameter or member 
'wext.ssid' not described in 'wireless_dev'
   include/net/cfg80211.h:4381: warning: Function parameter or member 
'wext.default_key' not described in 'wireless_dev'
   include/net/cfg80211.h:4381: warning: Function parameter or member 
'wext.default_mgmt_key' not described in 'wireless_dev'
   include/net/cfg80211.h:4381: warning: Function parameter or member 
'wext.prev_bssid_valid' not described in 'wireless_dev'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'
   include/net/cfg80211.h:4869: warning: Excess function parameter 'ptr' 
description in 'reg_query_regdb_wmm'

vim +2882 mm/filemap.c

  2851  
  2852  /**
  2853   * filemap_page_mkwrite_nommap_sem - handle dropping the mmap_sem and 
caching
  2854   *              the resulting page from the fs's mkwrite callback.
  2855   * @vmf:                struct vm_fault containing details of the fault
  2856   * @page_mkwrite_cb:    the fs specific mkwrite callback
  2857   *
  2858   * Some file systems have very heavy mkwrite operations, which means 
that we can
  2859   * hold the mmap_sem for long periods of time.  This can cause weird 
priority
  2860   * inversions in the system if something tries to take a write lock on 
the
  2861   * mmap_sem, which will block any new readers until the writer has done 
its
  2862   * work.
  2863   *
  2864   * This helper allows file systems to opt-in to a mechanism that will 
handle
  2865   * dropping the mmap_sem during the mkwrite, and then caching the 
result and
  2866   * re-using the page in the next loop through the fault handler as long 
as it is
  2867   * still valid.
  2868   *
  2869   * Users of this helper must be sure to _never_ access vmf->vma as it 
could be
  2870   * invalid, instead they need to access vmf->file as that will either 
be pinned
  2871   * because we grabbed a reference before dropping the mmap_sem, or we 
still have
  2872   * the mmap_sem and thus is still save to look at.
  2873   *
  2874   * vma->vm_mm->mmap-sem must be held on entry.
  2875   *
  2876   * If our return value has VM_FAULT_RETRY set then the mmap_sem has been
  2877   * dropped, otherwise it is still held.
  2878   */
  2879  vm_fault_t filemap_page_mkwrite_nommapsem(struct vm_fault *vmf,
  2880                                            page_mkwrite_cb *mkwrite)
  2881  {
> 2882          struct mm_struct *mm = vmf->vma->vm_mm;
  2883          struct page *page = vmf->page;
  2884          struct file *file = vmf->vma->vm_file;
  2885          struct file *fpin;
  2886          vm_fault_t ret;
  2887  
  2888          /*
  2889           * Our page is already initialized from a previous loop through 
the
  2890           * fault handler, so lock it and check if it is valid, and if 
it is
  2891           * simply return.
  2892           */
  2893          if (vmf->flags & FAULT_FLAG_PAGE_INITIALISED) {
  2894                  lock_page(page);
  2895                  if (initialised_page_valid(vmf, page))
  2896                          return VM_FAULT_LOCKED;
  2897                  unlock_page(page);
  2898          }
  2899  
  2900          /*
  2901           * mkwrite can be expensive, so drop the mmap_sem for this 
operation and
  2902           * deal with caching the page for the next trip around.
  2903           */
  2904          fpin = maybe_unlock_mmap_for_io(vmf->vma, vmf->flags);
  2905          vmf->file = file;
  2906          ret = mkwrite(vmf);
  2907          if (fpin) {
  2908                  if (ret == VM_FAULT_LOCKED)
  2909                          unlock_page(page);
  2910                  fput(fpin);
  2911  
  2912                  /*
  2913                   * We had an error when doing mkwrite, instead of 
looping
  2914                   * through again just down_read the mmap_sem and return 
the
  2915                   * error.  Otherwise cache the page for the next trip 
through.
  2916                   */
  2917                  if (ret & VM_FAULT_ERROR) {
  2918                          down_read(&mm->mmap_sem);
  2919                  } else {
  2920                          get_page(page);
  2921                          vmf->cached_page = page;
  2922                          ret = VM_FAULT_RETRY;
  2923                  }
  2924          }
  2925          return ret;
  2926  }
  2927  

---
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