Re: + fs-epoll-add-procfs-fdinfo-helper.patch added to -mm tree

[Cyrill Gorcunov]

On Tue, Nov 13, 2012 at 07:53:13PM +0400, Cyrill Gorcunov wrote:
> On Tue, Nov 13, 2012 at 03:50:50PM +0100, Oleg Nesterov wrote:
> > This doesn't look right.
> > 
> > The problem is, the current locking is broken, ->siglock can not serialize
> > ->sigmask changes. Just suppose the the child inherits sigfd from parent
> > and they both do sys_signalfd4() at the same time.
> > 
> > Nothing really bad can happen, that is why nobody bothers to fix this.
> > But this patch makes the thing worse, write_seqcount_begin() must be
> > serialized correctly.
> 
> Thanks a lot, Oleg! I'll update.

Something like below?
---
From: Cyrill Gorcunov <gorcu...@openvz.org>
Subject: fdinfo: Show sigmask for signalfd fd v3

Signed-off-by: Cyrill Gorcunov <gorcu...@openvz.org>
CC: Pavel Emelyanov <xe...@parallels.com>
CC: Al Viro <v...@zeniv.linux.org.uk>
CC: Alexey Dobriyan <adobri...@gmail.com>
CC: Andrew Morton <a...@linux-foundation.org>
CC: James Bottomley <jbottom...@parallels.com>
CC: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com>
CC: Alexey Dobriyan <adobri...@gmail.com>
CC: Matthew Helsley <matt.hels...@gmail.com>
CC: "J. Bruce Fields" <bfie...@fieldses.org>
CC: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com>
---
 fs/proc/array.c         |    2 +-
 fs/signalfd.c           |   24 ++++++++++++++++++++++++
 include/linux/proc_fs.h |    3 +++
 3 files changed, 28 insertions(+), 1 deletion(-)

Index: linux-2.6.git/fs/proc/array.c
===================================================================
--- linux-2.6.git.orig/fs/proc/array.c
+++ linux-2.6.git/fs/proc/array.c
@@ -220,7 +220,7 @@ static inline void task_state(struct seq
        seq_putc(m, '\n');
 }
 
-static void render_sigset_t(struct seq_file *m, const char *header,
+void render_sigset_t(struct seq_file *m, const char *header,
                                sigset_t *set)
 {
        int i;
Index: linux-2.6.git/fs/signalfd.c
===================================================================
--- linux-2.6.git.orig/fs/signalfd.c
+++ linux-2.6.git/fs/signalfd.c
@@ -29,6 +29,7 @@
 #include <linux/anon_inodes.h>
 #include <linux/signalfd.h>
 #include <linux/syscalls.h>
+#include <linux/proc_fs.h>
 
 void signalfd_cleanup(struct sighand_struct *sighand)
 {
@@ -46,6 +47,7 @@ void signalfd_cleanup(struct sighand_str
 }
 
 struct signalfd_ctx {
+       rwlock_t lock;
        sigset_t sigmask;
 };
 
@@ -227,7 +229,26 @@ static ssize_t signalfd_read(struct file
        return total ? total: ret;
 }
 
+#ifdef CONFIG_PROC_FS
+static int signalfd_show_fdinfo(struct seq_file *m, struct file *f)
+{
+       struct signalfd_ctx *ctx = f->private_data;
+       sigset_t sigmask;
+
+       read_lock(&ctx->lock);
+       sigmask = ctx->sigmask;
+       read_unlock(&ctx->lock);
+
+       signotset(&sigmask);
+       render_sigset_t(m, "sigmask:\t", &sigmask);
+       return 0;
+}
+#endif
+
 static const struct file_operations signalfd_fops = {
+#ifdef CONFIG_PROC_FS
+       .show_fdinfo    = signalfd_show_fdinfo,
+#endif
        .release        = signalfd_release,
        .poll           = signalfd_poll,
        .read           = signalfd_read,
@@ -259,6 +280,7 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sig
                        return -ENOMEM;
 
                ctx->sigmask = sigmask;
+               rwlock_init(&ctx->lock);
 
                /*
                 * When we call this, the initialization must be complete, since
@@ -278,7 +300,9 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sig
                        return -EINVAL;
                }
                spin_lock_irq(&current->sighand->siglock);
+               write_lock(&ctx->lock);
                ctx->sigmask = sigmask;
+               write_unlock(&ctx->lock);
                spin_unlock_irq(&current->sighand->siglock);
 
                wake_up(&current->sighand->signalfd_wqh);
Index: linux-2.6.git/include/linux/proc_fs.h
===================================================================
--- linux-2.6.git.orig/include/linux/proc_fs.h
+++ linux-2.6.git/include/linux/proc_fs.h
@@ -290,4 +290,7 @@ static inline struct net *PDE_NET(struct
        return pde->parent->data;
 }
 
+#include <linux/signal.h>
+
+void render_sigset_t(struct seq_file *m, const char *header, sigset_t *set);
 #endif /* _LINUX_PROC_FS_H */
--
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