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authorDipankar Sarma <dipankar@in.ibm.com>2005-09-09 13:04:13 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-09-09 13:57:55 -0700
commitab2af1f5005069321c5d130f09cce577b03f43ef (patch)
tree73a70ba486f522cd9eeeef376ede2b5a1c1b473b /fs/fcntl.c
parent6e72ad2c581de121cc7e772469e2a8f6b1fd4379 (diff)
downloadlinux-linaro-ab2af1f5005069321c5d130f09cce577b03f43ef.tar.gz
[PATCH] files: files struct with RCU
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>
Diffstat (limited to 'fs/fcntl.c')
-rw-r--r--fs/fcntl.c13
1 files changed, 10 insertions, 3 deletions
diff --git a/fs/fcntl.c b/fs/fcntl.c
index bfecc623808..d2f3ed8acd9 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -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);