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Groups > linux.kernel > #1573216 > unrolled thread
| Started by | "Steven Rostedt (VMware)" <rostedt@goodmis.org> |
|---|---|
| First post | 2017-02-03 17:00 +0100 |
| Last post | 2017-02-05 00:00 +0100 |
| Articles | 2 — 2 participants |
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[PATCH] shm: Fix unlikely() test of info->seals to test only for WRITE and GROW "Steven Rostedt (VMware)" <rostedt@goodmis.org> - 2017-02-03 17:00 +0100
Re: [PATCH] shm: Fix unlikely() test of info->seals to test only for WRITE and GROW Hugh Dickins <hughd@google.com> - 2017-02-05 00:00 +0100
| From | "Steven Rostedt (VMware)" <rostedt@goodmis.org> |
|---|---|
| Date | 2017-02-03 17:00 +0100 |
| Subject | [PATCH] shm: Fix unlikely() test of info->seals to test only for WRITE and GROW |
| Message-ID | <t6Orh-3Ei-53@gated-at.bofh.it> |
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Running my likely/unlikely profiler, I discovered that the test in
shmem_write_begin() that tests for info->seals as unlikely, is
always incorrect. This is because shmem_get_inode() sets info->seals to
have F_SEAL_SEAL set by default, and it is unlikely to be cleared when
shmem_write_begin() is called. Thus, the if statement is very likely.
But as the if statement block only cares about F_SEAL_WRITE and
F_SEAL_GROW, change the test to only test those two bits.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
mm/shmem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index bb53285..ef4cdbb 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2194,7 +2194,7 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
pgoff_t index = pos >> PAGE_SHIFT;
/* i_mutex is held by caller */
- if (unlikely(info->seals)) {
+ if (unlikely(info->seals & (F_SEAL_WRITE | F_SEAL_GROW))) {
if (info->seals & F_SEAL_WRITE)
return -EPERM;
if ((info->seals & F_SEAL_GROW) && pos + len > inode->i_size)
--
2.9.3
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| From | Hugh Dickins <hughd@google.com> |
|---|---|
| Date | 2017-02-05 00:00 +0100 |
| Subject | Re: [PATCH] shm: Fix unlikely() test of info->seals to test only for WRITE and GROW |
| Message-ID | <t7htf-7hT-9@gated-at.bofh.it> |
| In reply to | #1573216 |
On Fri, 3 Feb 2017, Steven Rostedt (VMware) wrote:
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
>
> Running my likely/unlikely profiler, I discovered that the test in
> shmem_write_begin() that tests for info->seals as unlikely, is
> always incorrect. This is because shmem_get_inode() sets info->seals to
> have F_SEAL_SEAL set by default, and it is unlikely to be cleared when
> shmem_write_begin() is called. Thus, the if statement is very likely.
>
> But as the if statement block only cares about F_SEAL_WRITE and
> F_SEAL_GROW, change the test to only test those two bits.
>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Hugh Dickins <hughd@google.com>
> ---
> mm/shmem.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index bb53285..ef4cdbb 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -2194,7 +2194,7 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
> pgoff_t index = pos >> PAGE_SHIFT;
>
> /* i_mutex is held by caller */
> - if (unlikely(info->seals)) {
> + if (unlikely(info->seals & (F_SEAL_WRITE | F_SEAL_GROW))) {
> if (info->seals & F_SEAL_WRITE)
> return -EPERM;
> if ((info->seals & F_SEAL_GROW) && pos + len > inode->i_size)
> --
> 2.9.3
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