how to fix is_local_disk()?
Subsystems (5)
In drivers/char/sysrq.c we have this nice piece of code:
/* do_emergency_sync helper function */
/* Guesses if the device is a local hard drive */ static int is_local_disk(struct block_device *bdev)
{
switch (MAJOR(bdev->bd_dev)) {
case IDE0_MAJOR:
<...>
case SCSI_DISK0_MAJOR:
<...>
case XT_DISK_MAJOR:
return 1;
default:
return 0;
}now this has a bunch of problems:
(1) it's horribly out of data. e.g. it only lists half of the scsi majors and nothing but ide and xt in addition to it. Second it tries to guess local disks by majors which obviously doesn't work with dynamic device number allocation or sub-major ranges. The easiest fix would be to add a GENHD_FL_LOCAL flags for struct gendisk so is_local_disk just becomes:
static int is_local_disk(struct block_device *bdev)
{
return (bdev->bd_disk->flags & GENHD_FL_LOCAL);
}but do we actually want to keep this code? And it yes shouldn't we have a reverse flag for don't emergency sync instead as the number of block drivers needing this is probably much much smaller..
Quoted 3 lines · Christoph Hellwig
In
drivers/char/sysrq.cwe have this nice piece of code:
Suggest you chainsaw the whole lot and simply do a wakeup_bdflush(0) from interrupt context.
The only functional change I can see with this is that it could cause pdflush to get stuck if there are dead NFS/SMBFS/etc mounts.
But if that happens, we need to fix it anyway. Those filesystems should avoid getting stuck if called with writeback_control.sync_mode != WB_SYNC_ALL, especially if current_is_pdflush() returns true.
Quoted 2 lines · Andrew Morton
Suggest you chainsaw the whole lot and simply do a
wakeup_bdflush(0)from interrupt context.
That's fine for the sync case but what about the remount r/o case?
Quoted 9 lines · Andrew Morton
Quoted 3 lines · Christoph Hellwig
In
drivers/char/sysrq.cwe have this nice piece of code:Suggest you chainsaw the whole lot and simply do a
wakeup_bdflush(0)from interrupt context.
Actually, that's a bit slack because it won't run journal commits and such. The below should do the trick.
But we still need superblock walking code to do the remount-ro thing. Another superblock-iterator which calls do_remount_sb()?
fs/buffer.c | 16 +++++++++++++--- include/linux/fs.h | 1 + 2 files changed, 14 insertions(+), 3 deletions(-)
fs/buffer.c renamed from fs/buffer.c~emergency_sync +13 -3
@@ -244,18 +244,28 @@ int fsync_bdev(struct block_device *bdev* sync everything. Start out by waking pdflush, because that writes back * all queues in parallel. */ -asmlinkage long sys_sync (void ) +static void do_sync (unsigned long wait) {wakeup_bdflush (0 );sync_inodes (0 );/* All mappings, inodes and their blockdevs */ DQUOT_SYNC (NULL );sync_supers ();/* Write the superblocks */ sync_filesystems (0 );/* Start syncing the filesystems */ -sync_filesystems (1 );/* Waitingly sync the filesystems */ -sync_inodes (1 );/* Mappings, inodes and blockdevs, again. */ +sync_filesystems (wait);/* Waitingly sync the filesystems */ +sync_inodes (wait);/* Mappings, inodes and blockdevs, again. */ +} + +asmlinkage long sys_sync (void ) +{ +do_sync (1 );return 0 ; } +void emergency_sync (void ) +{ +pdflush_operation (do_sync,0 ); +} +/* * Generic function to fsync a file. *
include/linux/fs.h renamed from include/linux/fs.h~emergency_sync +1 -0
@@ -1113,6 +1113,7 @@ extern int filemap_flush(struct address_extern int filemap_fdatawait (struct address_space *);extern void sync_supers (void );extern void sync_filesystems (int wait); +extern void emergency_sync (void );extern sector_t bmap (struct inode *,sector_t );extern int setattr_mask (unsigned int );extern int notify_change (struct dentry *,struct iattr *);
_
Quoted 4 lines · Andrew Morton
The below should do the trick.
But we still need superblock walking code to do the remount-ro thing. Another superblock-iterator which calls
do_remount_sb()?
Yupp, patch below. The iterator is in fs/super.c to allow sharing a piece of code with the normal remount path and to avoid forgetting it when updating the locking rules like approximately the last two years. Works fine here but I'm not sure what we want to do with panic()..
drivers/char/sysrq.c +5 -117
@@ -101,131 +101,19 @@ {machine_restart (NULL ); } +static struct sysrq_key_op sysrq_reboot_op = { .handler = sysrq_handle_reboot, .help_msg ="reBoot" , .action_msg ="Resetting" , }; - - -/* SYNC SYSRQ HANDLERS BLOCK */ - -/* do_emergency_sync helper function */ -/* Guesses if the device is a local hard drive */ -static int is_local_disk (struct block_device *bdev) -{ -switch (MAJOR (bdev->bd_dev)) { -case IDE0_MAJOR : -case IDE1_MAJOR : -case IDE2_MAJOR : -case IDE3_MAJOR : -case IDE4_MAJOR : -case IDE5_MAJOR : -case IDE6_MAJOR : -case IDE7_MAJOR : -case IDE8_MAJOR : -case IDE9_MAJOR : -case SCSI_DISK0_MAJOR : -case SCSI_DISK1_MAJOR : -case SCSI_DISK2_MAJOR : -case SCSI_DISK3_MAJOR : -case SCSI_DISK4_MAJOR : -case SCSI_DISK5_MAJOR : -case SCSI_DISK6_MAJOR : -case SCSI_DISK7_MAJOR : -case XT_DISK_MAJOR : -return 1 ; -default : -return 0 ; - } -} - -/* do_emergency_sync helper function */ -static void go_sync (struct super_block *sb,int remount_flag) -{ -int orig_loglevel; - orig_loglevel = console_loglevel; - console_loglevel =7 ; -printk (KERN_INFO "%sing device %s ... " , - remount_flag ?"Remount" :"Sync" , - sb->s_id); - -if (remount_flag) {/* Remount R/O */ -int ret, flags; -struct file *file; - -if (sb->s_flags &MS_RDONLY ) { -printk ("R/O\n" ); -return ; - } - -file_list_lock (); -list_for_each_entry (file, &sb->s_files, f_list) { -if (file->f_dentry &&file_count (file) - &&S_ISREG (file->f_dentry->d_inode->i_mode)) - file->f_mode &= ~2 ; - } -file_list_unlock (); -DQUOT_OFF (sb); -fsync_bdev (sb->s_bdev); - flags =MS_RDONLY ; -if (sb->s_op && sb->s_op->remount_fs) { - ret = sb->s_op->remount_fs (sb, &flags,NULL ); -if (ret) -printk ("error %d\n" , ret); -else { - sb->s_flags = (sb->s_flags & ~MS_RMT_MASK ) | (flags &MS_RMT_MASK ); -printk ("OK\n" ); - } - }else -printk ("nothing to do\n" ); - }else {/* Sync only */ -fsync_bdev (sb->s_bdev); -printk ("OK\n" ); - } - console_loglevel = orig_loglevel; -} -/* -* Emergency Sync or Unmount. We cannot do it directly, so we set a special -* flag and wake up the bdflush kernel thread which immediately calls this function. -* We process all mounted hard drives first to recover from crashed experimental -* block devices and malfunctional network filesystems. -*/ - -int emergency_sync_scheduled; - -void do_emergency_sync (void ) { -struct super_block *sb; -int remount_flag; -int orig_loglevel; - -lock_kernel (); - remount_flag = (emergency_sync_scheduled ==EMERG_REMOUNT ); - emergency_sync_scheduled =0 ; - -list_for_each_entry (sb, &super_blocks, s_list) -if (sb->s_bdev &&is_local_disk (sb->s_bdev)) -go_sync (sb, remount_flag); - -list_for_each_entry (sb, &super_blocks, s_list) -if (sb->s_bdev && !is_local_disk (sb->s_bdev)) -go_sync (sb, remount_flag); - -unlock_kernel (); - - orig_loglevel = console_loglevel; - console_loglevel =7 ; -printk (KERN_INFO "Done.\n" ); - console_loglevel = orig_loglevel; -} -static void sysrq_handle_sync (int key,struct pt_regs *pt_regs,struct tty_struct *tty) { - emergency_sync_scheduled =EMERG_SYNC ; -wakeup_bdflush (0 ); +emergency_sync (); } +static struct sysrq_key_op sysrq_sync_op = { .handler = sysrq_handle_sync, .help_msg ="Sync" ,
@@ -235,9 +123,9 @@static void sysrq_handle_mountro (int key,struct pt_regs *pt_regs,struct tty_struct *tty) { - emergency_sync_scheduled =EMERG_REMOUNT ; -wakeup_bdflush (0 ); +emergency_remount (); } +static struct sysrq_key_op sysrq_mountro_op = { .handler = sysrq_handle_mountro, .help_msg ="Unmount" ,
fs/buffer.c +13 -3
@@ -244,16 +244,26 @@* sync everything. Start out by waking pdflush, because that writes back * all queues in parallel. */ -asmlinkage long sys_sync (void ) +static void do_sync (unsigned long wait) {wakeup_bdflush (0 );sync_inodes (0 );/* All mappings, inodes and their blockdevs */ DQUOT_SYNC (NULL );sync_supers ();/* Write the superblocks */ sync_filesystems (0 );/* Start syncing the filesystems */ -sync_filesystems (1 );/* Waitingly sync the filesystems */ -sync_inodes (1 );/* Mappings, inodes and blockdevs, again. */ +sync_filesystems (wait);/* Waitingly sync the filesystems */ +sync_inodes (wait);/* Mappings, inodes and blockdevs, again. */ +} + +asmlinkage long sys_sync (void ) +{ +do_sync (1 );return 0 ; +} + +void emergency_sync (void ) +{ +pdflush_operation (do_sync,0 ); }/*
fs/namespace.c +3 -3
@@ -24,7 +24,7 @@#include <asm/uaccess.h> extern struct vfsmount *do_kern_mount (const char *type,int flags,char *name,void *data); -extern int do_remount_sb (struct super_block *sb,int flags,void * data); +extern int do_remount_sb (struct super_block *sb,int flags,void *data,int force);extern int __init init_rootfs (void );extern int __init fs_subsys_init (void );
@@ -326,7 +326,7 @@down_write (&sb->s_umount);if (!(sb->s_flags &MS_RDONLY )) {lock_kernel (); - retval =do_remount_sb (sb,MS_RDONLY ,0 ); + retval =do_remount_sb (sb,MS_RDONLY ,0 ,0 );unlock_kernel (); }up_write (&sb->s_umount);
@@ -555,7 +555,7 @@return -EINVAL ;down_write (&sb->s_umount); - err =do_remount_sb (sb, flags, data); + err =do_remount_sb (sb, flags, data,0 );if (!err) nd->mnt->mnt_flags=mnt_flags;up_write (&sb->s_umount);
fs/super.c +44 -5
90 lines not on this page · raw message
include/linux/fs.h +2 -0
@@ -1113,6 +1113,8 @@extern int filemap_fdatawait (struct address_space *);extern void sync_supers (void );extern void sync_filesystems (int wait); +extern void emergency_sync (void ); +extern void emergency_remount (void );extern sector_t bmap (struct inode *,sector_t );extern int setattr_mask (unsigned int );extern int notify_change (struct dentry *,struct iattr *);
include/linux/sysrq.h +0 -18
@@ -92,21 +92,3 @@#define unregister_sysrq_key (ig,nore) __reterr()#endif - - -/* Deferred actions */ - -extern int emergency_sync_scheduled; - -#define EMERG_SYNC 1 -#define EMERG_REMOUNT 2 - -void do_emergency_sync (void ); - -#ifdef CONFIG_MAGIC_SYSRQ -#define CHECK_EMERGENCY_SYNC \ - if (emergency_sync_scheduled) \ - do_emergency_sync(); -#else -#define CHECK_EMERGENCY_SYNC -#endif
kernel/panic.c +2 -3
@@ -96,9 +96,8 @@disabled_wait (caller);#endif local_irq_enable (); -for (;;) { - CHECK_EMERGENCY_SYNC - } +for (;;) + ; }/**
mm/page-writeback.c +0 -2
@@ -20,7 +20,6 @@#include <linux/pagemap.h> #include <linux/writeback.h> #include <linux/init.h> -#include <linux/sysrq.h> #include <linux/backing-dev.h> #include <linux/blkdev.h> #include <linux/mpage.h>
@@ -237,7 +236,6 @@ .nonblocking = 1, }; -CHECK_EMERGENCY_SYNC for ( ; ; ) {struct page_state ps;long background_thresh;
Quoted 4 lines · Christoph Hellwig
...
fs/super.c +2
-0+static void do_emergency_remount (unsigned long foo) +{
fs/super.c line 496
Quoted 10 lines
fs/super.c +10
-0+struct super_block *sb; + +spin_lock (&sb_lock); +list_for_each_entry (sb, &super_blocks, s_list) { + sb->s_count++; +spin_unlock (&sb_lock); +down_read (&sb->s_umount); +if (sb->s_bdev && !(sb->s_flags &MS_RDONLY )) +do_remount_sb (sb,MS_RDONLY ,NULL ,1 ); +drop_super (sb);
You might need to check sb->s_root in here after acquiring sb->s_umount. Otherwise the fs may have been unmounted while the semaphore was being waited upon.
About half of the s_umount grabbers perform that check. The others might be buggy. I'm not sure - it's all rather gunky in there and hard to tell what the rules are.
Quoted 3 lines · Andrew Morton
About half of the
s_umountgrabbers perform that check. The others might be buggy. I'm not sure - it's all rather gunky in there and hard to tell what the rules are.
Very simple, actually - if you are holding an active reference, no checks are needed. If you do not (as in this case) - you need to check that filesystem is not in the middle of shutdown after getting ->s_umount.