do_sys_poll: simplify playing with on-stack data

Cleanup. Lessens both the source and compiled code (100 bytes) and imho makes the code much more understandable. With this patch "struct poll_list *head" always points to on-stack stack_pps, so we can remove all "is it on-stack" and "was it initialized" checks. Also, move poll_initwait/poll_freewait and -EINTR detection closer to the do_poll()'s callsite. [akpm@linux-foundation.org: fix warning (size_t != uint)] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Looks-good-to: Andi Kleen <ak@suse.de> Cc: Davide Libenzi <davidel@xmailserver.org> Cc: Vadim Lobanov <vlobanov@speakeasy.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

do_sys_poll: simplify playing with on-stack data
Cleanup. Lessens both the source and compiled code (100 bytes) and imho makes the code much more understandable. With this patch "struct poll_list *head" always points to on-stack stack_pps, so we can remove all "is it on-stack" and "was it initialized" checks. Also, move poll_initwait/poll_freewait and -EINTR detection closer to the do_poll()'s callsite. [akpm@linux-foundation.org: fix warning (size_t != uint)] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Looks-good-to: Andi Kleen <ak@suse.de> Cc: Davide Libenzi <davidel@xmailserver.org> Cc: Vadim Lobanov <vlobanov@speakeasy.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Oleg Nesterov · Linus Torvalds
1 parent 759d7c6c47
Showing 1 changed file with 36 additions and 56 deletions Side-by-side Diff
fs/select.c
@@ -651,86 +651,66 @@
 int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout)
 {
 	struct poll_wqueues table;
- 	int fdcount, err;
- 	unsigned int i;
-	struct poll_list *head;
- 	struct poll_list *walk;
+ 	int err = -EFAULT, fdcount, len, size;
 	/* Allocate small arguments on the stack to save memory and be
 	   faster - use long to make sure the buffer is aligned properly
 	   on 64 bit archs to avoid unaligned access */
 	long stack_pps[POLL_STACK_ALLOC/sizeof(long)];
-	struct poll_list *stack_pp = NULL;
+	struct poll_list *const head = (struct poll_list *)stack_pps;
+ 	struct poll_list *walk = head;
+ 	unsigned long todo = nfds;
  
-	/* Do a sanity check on nfds ... */
 	if (nfds > current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
 		return -EINVAL;
  
-	poll_initwait(&table);
+	len = min_t(unsigned int, nfds, N_STACK_PPS);
+	for (;;) {
+		walk->next = NULL;
+		walk->len = len;
+		if (!len)
+			break;
  
-	head = NULL;
-	walk = NULL;
-	i = nfds;
-	err = -ENOMEM;
-	while(i!=0) {
-		struct poll_list *pp;
-		int num, size;
-		if (stack_pp == NULL)
-			num = N_STACK_PPS;
-		else
-			num = POLLFD_PER_PAGE;
-		if (num > i)
-			num = i;
-		size = sizeof(struct poll_list) + sizeof(struct pollfd)*num;
-		if (!stack_pp)
-			stack_pp = pp = (struct poll_list *)stack_pps;
-		else {
-			pp = kmalloc(size, GFP_KERNEL);
-			if (!pp)
-				goto out_fds;
-		}
-		pp->next=NULL;
-		pp->len = num;
-		if (head == NULL)
-			head = pp;
-		else
-			walk->next = pp;
+		if (copy_from_user(walk->entries, ufds + nfds-todo,
+					sizeof(struct pollfd) * walk->len))
+			goto out_fds;
  
-		walk = pp;
-		if (copy_from_user(pp->entries, ufds + nfds-i, 
-				sizeof(struct pollfd)*num)) {
-			err = -EFAULT;
+		todo -= walk->len;
+		if (!todo)
+			break;
+
+		len = min(todo, POLLFD_PER_PAGE);
+		size = sizeof(struct poll_list) + sizeof(struct pollfd) * len;
+		walk = walk->next = kmalloc(size, GFP_KERNEL);
+		if (!walk) {
+			err = -ENOMEM;
 			goto out_fds;
 		}
-		i -= pp->len;
 	}
  
+	poll_initwait(&table);
 	fdcount = do_poll(nfds, head, &table, timeout);
+	if (!fdcount && signal_pending(current))
+		fdcount = -EINTR;
+	poll_freewait(&table);
  
-	/* OK, now copy the revents fields back to user space. */
-	walk = head;
-	err = -EFAULT;
-	while(walk != NULL) {
+	for (walk = head; walk; walk = walk->next) {
 		struct pollfd *fds = walk->entries;
 		int j;
  
-		for (j=0; j < walk->len; j++, ufds++) {
-			if(__put_user(fds[j].revents, &ufds->revents))
+		for (j = 0; j < walk->len; j++, ufds++)
+			if (__put_user(fds[j].revents, &ufds->revents))
 				goto out_fds;
-		}
-		walk = walk->next;
   	}
+
 	err = fdcount;
-	if (!fdcount && signal_pending(current))
-		err = -EINTR;
 out_fds:
-	walk = head;
-	while(walk!=NULL) {
-		struct poll_list *pp = walk->next;
-		if (walk != stack_pp)
-			kfree(walk);
-		walk = pp;
+	walk = head->next;
+	while (walk) {
+		struct poll_list *pos = walk;
+		walk = walk->next;
+		kfree(pos);
 	}
-	poll_freewait(&table);
+
 	return err;
 }
...	...	@@ -651,86 +651,66 @@
651	651	int do_sys_poll(struct pollfd __user ufds, unsigned int nfds, s64 timeout)
652	652	{
653	653	struct poll_wqueues table;
654		- int fdcount, err;
655		- unsigned int i;
656		- struct poll_list *head;
657		- struct poll_list *walk;
	654	+ int err = -EFAULT, fdcount, len, size;
658	655	/* Allocate small arguments on the stack to save memory and be
659	656	faster - use long to make sure the buffer is aligned properly
660	657	on 64 bit archs to avoid unaligned access */
661	658	long stack_pps[POLL_STACK_ALLOC/sizeof(long)];
662		- struct poll_list *stack_pp = NULL;
	659	+ struct poll_list const head = (struct poll_list )stack_pps;
	660	+ struct poll_list *walk = head;
	661	+ unsigned long todo = nfds;
663	662
664		- /* Do a sanity check on nfds ... */
665	663	if (nfds > current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
666	664	return -EINVAL;
667	665
668		- poll_initwait(&table);
	666	+ len = min_t(unsigned int, nfds, N_STACK_PPS);
	667	+ for (;;) {
	668	+ walk->next = NULL;
	669	+ walk->len = len;
	670	+ if (!len)
	671	+ break;
669	672
670		- head = NULL;
671		- walk = NULL;
672		- i = nfds;
673		- err = -ENOMEM;
674		- while(i!=0) {
675		- struct poll_list *pp;
676		- int num, size;
677		- if (stack_pp == NULL)
678		- num = N_STACK_PPS;
679		- else
680		- num = POLLFD_PER_PAGE;
681		- if (num > i)
682		- num = i;
683		- size = sizeof(struct poll_list) + sizeof(struct pollfd)*num;
684		- if (!stack_pp)
685		- stack_pp = pp = (struct poll_list *)stack_pps;
686		- else {
687		- pp = kmalloc(size, GFP_KERNEL);
688		- if (!pp)
689		- goto out_fds;
690		- }
691		- pp->next=NULL;
692		- pp->len = num;
693		- if (head == NULL)
694		- head = pp;
695		- else
696		- walk->next = pp;
	673	+ if (copy_from_user(walk->entries, ufds + nfds-todo,
	674	+ sizeof(struct pollfd) * walk->len))
	675	+ goto out_fds;
697	676
698		- walk = pp;
699		- if (copy_from_user(pp->entries, ufds + nfds-i,
700		- sizeof(struct pollfd)*num)) {
701		- err = -EFAULT;
	677	+ todo -= walk->len;
	678	+ if (!todo)
	679	+ break;
	680	+
	681	+ len = min(todo, POLLFD_PER_PAGE);
	682	+ size = sizeof(struct poll_list) + sizeof(struct pollfd) * len;
	683	+ walk = walk->next = kmalloc(size, GFP_KERNEL);
	684	+ if (!walk) {
	685	+ err = -ENOMEM;
702	686	goto out_fds;
703	687	}
704		- i -= pp->len;
705	688	}
706	689
	690	+ poll_initwait(&table);
707	691	fdcount = do_poll(nfds, head, &table, timeout);
	692	+ if (!fdcount && signal_pending(current))
	693	+ fdcount = -EINTR;
	694	+ poll_freewait(&table);
708	695
709		- /* OK, now copy the revents fields back to user space. */
710		- walk = head;
711		- err = -EFAULT;
712		- while(walk != NULL) {
	696	+ for (walk = head; walk; walk = walk->next) {
713	697	struct pollfd *fds = walk->entries;
714	698	int j;
715	699
716		- for (j=0; j < walk->len; j++, ufds++) {
717		- if(__put_user(fds[j].revents, &ufds->revents))
	700	+ for (j = 0; j < walk->len; j++, ufds++)
	701	+ if (__put_user(fds[j].revents, &ufds->revents))
718	702	goto out_fds;
719		- }
720		- walk = walk->next;
721	703	}
	704	+
722	705	err = fdcount;
723		- if (!fdcount && signal_pending(current))
724		- err = -EINTR;
725	706	out_fds:
726		- walk = head;
727		- while(walk!=NULL) {
728		- struct poll_list *pp = walk->next;
729		- if (walk != stack_pp)
730		- kfree(walk);
731		- walk = pp;
	707	+ walk = head->next;
	708	+ while (walk) {
	709	+ struct poll_list *pos = walk;
	710	+ walk = walk->next;
	711	+ kfree(pos);
732	712	}
733		- poll_freewait(&table);
	713	+
734	714	return err;
735	715	}
736	716