Messages in this thread | | | Date | Thu, 08 Sep 2005 11:37:07 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH 1/2] (repost) New System call, unshare (fwd) |
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Janak Desai wrote:
> - tsk->min_flt = tsk->maj_flt = 0; > - tsk->nvcsw = tsk->nivcsw = 0; > + /* > + * If the process memory is being duplicated as part of the > + * unshare system call, we are working with the current process > + * and not a newly allocated task strucutre, and should not > + * zero out fault info, context switch counts, mm and active_mm > + * fields. > + */ > + if (copy_share_action == MAY_SHARE) { > + tsk->min_flt = tsk->maj_flt = 0; > + tsk->nvcsw = tsk->nivcsw = 0; >
Why don't you just do this in copy_process?
> - tsk->mm = NULL; > - tsk->active_mm = NULL; > + tsk->mm = NULL; > + tsk->active_mm = NULL; > + } > > /* > * Are we cloning a kernel thread? > @@ -1002,7 +1023,7 @@ static task_t *copy_process(unsigned lon > goto bad_fork_cleanup_fs; > if ((retval = copy_signal(clone_flags, p))) > goto bad_fork_cleanup_sighand; > - if ((retval = copy_mm(clone_flags, p))) > + if ((retval = copy_mm(clone_flags, p, MAY_SHARE))) > goto bad_fork_cleanup_signal; > if ((retval = copy_keys(clone_flags, p))) > goto bad_fork_cleanup_mm; > @@ -1317,3 +1338,172 @@ void __init proc_caches_init(void) > sizeof(struct mm_struct), 0, > SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL); > } > + > +/* > + * unshare_mm is called from the unshare system call handler function to > + * make a private copy of the mm_struct structure. It calls copy_mm with > + * CLONE_VM flag cleard, to ensure that a private copy of mm_struct is made, > + * and with mm_copy_share enum set to UNSHARE, to ensure that copy_mm > + * does not clear fault info, context switch counts, mm and active_mm > + * fields of the mm_struct. > + */ > +static int unshare_mm(unsigned long unshare_flags, struct task_struct *tsk) > +{ > + int retval = 0; > + struct mm_struct *mm = tsk->mm; > + > + /* > + * If the virtual memory is being shared, make a private > + * copy and disassociate the process from the shared virtual > + * memory. > + */ > + if (atomic_read(&mm->mm_users) > 1) { > + retval = copy_mm((unshare_flags & ~CLONE_VM), tsk, UNSHARE); > + > + /* > + * If copy_mm was successful, decrement the number of users > + * on the original, shared, mm_struct. > + */ > + if (!retval) > + atomic_dec(&mm->mm_users); > + } > + return retval; > +} > +
What prevents thread 1 from decrementing mm_users after thread 2 has found it to be 2?
-- SUSE Labs, Novell Inc.
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