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[PATCH] files: files struct with RCU

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Patch to eliminate struct files_struct.file_lock spinlock on the reader side
and use rcu refcounting rcuref_xxx api for the f_count refcounter.  The
updates to the fdtable are done by allocating a new fdtable structure and
setting files->fdt to point to the new structure.  The fdtable structure is
protected by RCU thereby allowing lock-free lookup.  For fd arrays/sets that
are vmalloced, we use keventd to free them since RCU callbacks can't sleep.  A
global list of fdtable to be freed is not scalable, so we use a per-cpu list.
If keventd is already handling the current cpu's work, we use a timer to defer
queueing of that work.

Since the last publication, this patch has been re-written to avoid using
explicit memory barriers and use rcu_assign_pointer(), rcu_dereference()
premitives instead.  This required that the fd information is kept in a
separate structure (fdtable) and updated atomically.

Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Dipankar Sarma
2005-09-09 13:04:13 -07:00
committed by Linus Torvalds
parent 6e72ad2c58
commit ab2af1f500
10 changed files with 354 additions and 175 deletions
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13
fs/fcntl.c
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@@ -16,6 +16,7 @@
#include <linux/security.h>
#include <linux/ptrace.h>
#include <linux/signal.h>
#include <linux/rcupdate.h>
#include <asm/poll.h>
#include <asm/siginfo.h>
@@ -64,8 +65,8 @@ static int locate_fd(struct files_struct *files,
if (orig_start >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
goto out;
fdt = files_fdtable(files);
repeat:
fdt = files_fdtable(files);
/*
* Someone might have closed fd's in the range
* orig_start..fdt->next_fd
@@ -95,9 +96,15 @@ repeat:
if (error)
goto repeat;
/*
* We reacquired files_lock, so we are safe as long as
* we reacquire the fdtable pointer and use it while holding
* the lock, no one can free it during that time.
*/
fdt = files_fdtable(files);
if (start <= fdt->next_fd)
fdt->next_fd = newfd + 1;
error = newfd;
out:
@@ -163,7 +170,7 @@ asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
if (!tofree && FD_ISSET(newfd, fdt->open_fds))
goto out_fput;
fdt->fd[newfd] = file;
rcu_assign_pointer(fdt->fd[newfd], file);
FD_SET(newfd, fdt->open_fds);
FD_CLR(newfd, fdt->close_on_exec);
spin_unlock(&files->file_lock);