SB_START_PAGEFAULT(9) The Linux VFS SB_START_PAGEFAULT(9)NAME
sb_start_pagefault - get write access to a superblock from a page fault
SYNOPSIS
void sb_start_pagefault(struct super_block * sb);
ARGUMENTS
sb
the super we write to
DESCRIPTION
When a process starts handling write page fault, it should embed the operation into sb_start_pagefault - sb_end_pagefault 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.
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 sb_start_pagefault close to mmap_sem in lock ordering. Page fault
HANDLING CODE IMPLIES LOCK DEPENDENCY
mmap_sem -> sb_start_pagefault
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 SB_START_PAGEFAULT(9)
Check Out this Related Man Page
FREEZE_SUPER(9) The Linux VFS FREEZE_SUPER(9)NAME
freeze_super - lock the filesystem and force it into a consistent state
SYNOPSIS
int freeze_super(struct super_block * sb);
ARGUMENTS
sb
the super to lock
DESCRIPTION
Syncs the super to make sure the filesystem is consistent and calls the fs's freeze_fs. Subsequent calls to this without first thawing the
fs will return -EBUSY.
During this function, sb->s_writers.frozen goes through these values:
SB_UNFROZEN
File system is normal, all writes progress as usual.
SB_FREEZE_WRITE
The file system is in the process of being frozen. New writes should be blocked, though page faults are still allowed. We wait for all
writes to complete and then proceed to the next stage.
SB_FREEZE_PAGEFAULT
Freezing continues. Now also page faults are blocked but internal fs threads can still modify the filesystem (although they should not
dirty new pages or inodes), writeback can run etc. After waiting for all running page faults we sync the filesystem which will clean all
dirty pages and inodes (no new dirty pages or inodes can be created when sync is running).
SB_FREEZE_FS
The file system is frozen. Now all internal sources of fs modification are blocked (e.g. XFS preallocation truncation on inode reclaim).
This is usually implemented by blocking new transactions for filesystems that have them and need this additional guard. After all internal
writers are finished we call ->freeze_fs to finish filesystem freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
mostly auxiliary for filesystems to verify they do not modify frozen fs.
sb->s_writers.frozen is protected by sb->s_umount.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 FREEZE_SUPER(9)
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