Messages in this thread Patch in this message | | | Date | Mon, 2 Jul 2012 06:11:55 +0100 | From | Al Viro <> | Subject | Re: [PATCH 0/4] Was: deferring __fput() |
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On Mon, Jul 02, 2012 at 04:43:10AM +0100, Al Viro wrote: > On Sun, Jul 01, 2012 at 09:46:31PM -0400, Mimi Zohar wrote: > > On Sun, 2012-07-01 at 21:57 +0100, Al Viro wrote: > > > On Sun, Jul 01, 2012 at 03:50:02PM -0400, Mimi Zohar wrote: > > > > Replacing it with a call to __fput(), the system boots. > > > > > > "it" being just the part under that if (unlikely(...)))? Very interesting... If so, we > > > have some kernel thread ending up with delayed __fput() which somehow makes dracut (assuimg > > > you are using fedora initramfs to go with fedora config) unhappy. With your own patch, > > > doing async __fput() in a lot of cases when this one doesn't delay past the return to > > > userland managing to survive the boot... I wonder which files end up triggering that fun > > > and which kernel thread is responsible... Could you slap a printk() in there, showing > > > file->f_dentry->d_inode->i_mode (octal) and at least file->f_dentry->d_name.name? > > > Along with the current->comm[], all under that inner if (). And see which ones end up > > > going that way by the time execve() of /sbin/init fails. > > > > pid=1 uid=0 d_name=init comm=swapper/0 dev="rootfs" mode=100775 > > pid=1 uid=0 d_name=bash comm=swapper/0 dev="rootfs" mode=100755 > > OK... Here's what I suspect is going on: > * populating initramfs writes binaries there. We open files (for write) from > the kernel thread (there's nothing other than kernel threads at that point), write to > them, then close(). Final fput() gets delayed. > * Then we proceed to execve(). Which means mapping the binary with MAP_DENYWRITE. > Which fails, since there's a struct file still opened for write on that sucker. > > Your patch did not delay those fput() - they were done without ->mmap_sem held. So > it survived. Booting without initramfs always survives; booting with initramfs may > or may not survive, depending on the timings - if that scheduled work manages to > run by the time we do those execve(), we win. Note that async_synchronize_full() > done in init_post() might easily affect that, depending on config. > > As a quick test, could you try slapping a delay somewhere around the beginning > of init_post() and see if it rescues the system?
Ho-hum... How about this (modulo missing documentation of the whole sad mess):
diff --git a/fs/file_table.c b/fs/file_table.c index 470da0b..00fd849 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -284,6 +284,11 @@ static void ____fput(struct callback_head *work) __fput(container_of(work, struct file, f_u.fu_rcuhead)); } +void flush_delayed_fput(void) +{ + delayed_fput(NULL); +} + static DECLARE_WORK(delayed_fput_work, delayed_fput); void fput(struct file *file) diff --git a/include/linux/file.h b/include/linux/file.h index 58bf158..d9a4f5a 100644 --- a/include/linux/file.h +++ b/include/linux/file.h @@ -39,4 +39,6 @@ extern void put_unused_fd(unsigned int fd); extern void fd_install(unsigned int fd, struct file *file); +extern void flush_delayed_fput(void); + #endif /* __LINUX_FILE_H */ diff --git a/init/main.c b/init/main.c index b5cc0a7..3f151f6 100644 --- a/init/main.c +++ b/init/main.c @@ -68,6 +68,7 @@ #include <linux/shmem_fs.h> #include <linux/slab.h> #include <linux/perf_event.h> +#include <linux/file.h> #include <asm/io.h> #include <asm/bugs.h> @@ -804,8 +805,8 @@ static noinline int init_post(void) system_state = SYSTEM_RUNNING; numa_default_policy(); - current->signal->flags |= SIGNAL_UNKILLABLE; + flush_delayed_fput(); if (ramdisk_execute_command) { run_init_process(ramdisk_execute_command);
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