'\" t
.\"     Title: sb_start_pagefault
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: March 2017
.\"    Manual: The Linux VFS
.\"    Source: Kernel Hackers Manual 4.10.7
.\"  Language: English
.\"
.TH "SB_START_PAGEFAULT" "9" "March 2017" "Kernel Hackers Manual 4\&.10\&" "The Linux VFS"
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.SH "NAME"
sb_start_pagefault \- get write access to a superblock from a page fault
.SH "SYNOPSIS"
.HP \w'void\ sb_start_pagefault('u
.BI "void sb_start_pagefault(struct\ super_block\ *\ " "sb" ");"
.SH "ARGUMENTS"
.PP
\fIsb\fR
.RS 4
the super we write to
.RE
.SH "DESCRIPTION"
.PP
When a process starts handling write page fault, it should embed the operation into
\fBsb_start_pagefault\fR
\-
\fBsb_end_pagefault\fR
pair to get exclusion against file system freezing\&. This is needed since the page fault is going to dirty a page\&. This function increments number of running page faults preventing freezing\&. If the file system is already frozen, the function waits until the file system is thawed\&.
.PP
Since page fault freeze protection behaves as a lock, users have to preserve ordering of freeze protection and other filesystem locks\&. It is advised to put
\fBsb_start_pagefault\fR
close to mmap_sem in lock ordering\&. Page fault handling code implies lock dependency:
.PP
mmap_sem \-> sb_start_pagefault
.SH "COPYRIGHT"
.br