Hello everyone,
Please pull the following commit (263782c1c95bbddbb022dc092fd89a36bb8d5577)
from git://git.kvack.org/aio-fixes.git to fix an aio bug reported by Robert
Elliot.
---
As of commit f8567a3845ac05bb28f3c1b478ef752762bd39ef it is now possible to
have put_reqs_available() called from irq context. While put_reqs_available()
is per cpu, it did not protect itself from interrupts on the same CPU. This
lead to aio_complete() corrupting the available io requests count when run
under a heavy O_DIRECT workloads as reported by Robert Elliott. Fix this by
disabling irq updates around the per cpu batch updates of reqs_available.
Many thanks to Robert and folks for testing and tracking this down.
Reported-by: Robert Elliot <[email protected]>
Tested-by: Robert Elliot <[email protected]>
Signed-off-by: Benjamin LaHaise <[email protected]>
Cc: Jens Axboe <[email protected]>, Christoph Hellwig <[email protected]>
Cc: [email protected]
---
fs/aio.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/fs/aio.c b/fs/aio.c
index 955947e..1c9c5f0 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -830,16 +830,20 @@ void exit_aio(struct mm_struct *mm)
static void put_reqs_available(struct kioctx *ctx, unsigned nr)
{
struct kioctx_cpu *kcpu;
+ unsigned long flags;
preempt_disable();
kcpu = this_cpu_ptr(ctx->cpu);
+ local_irq_save(flags);
kcpu->reqs_available += nr;
+
while (kcpu->reqs_available >= ctx->req_batch * 2) {
kcpu->reqs_available -= ctx->req_batch;
atomic_add(ctx->req_batch, &ctx->reqs_available);
}
+ local_irq_restore(flags);
preempt_enable();
}
@@ -847,10 +851,12 @@ static bool get_reqs_available(struct kioctx *ctx)
{
struct kioctx_cpu *kcpu;
bool ret = false;
+ unsigned long flags;
preempt_disable();
kcpu = this_cpu_ptr(ctx->cpu);
+ local_irq_save(flags);
if (!kcpu->reqs_available) {
int old, avail = atomic_read(&ctx->reqs_available);
@@ -869,6 +875,7 @@ static bool get_reqs_available(struct kioctx *ctx)
ret = true;
kcpu->reqs_available--;
out:
+ local_irq_restore(flags);
preempt_enable();
return ret;
}
--
1.8.2.1
--
"Thought is the essence of where you are now."
On 2014-07-14 19:12, Benjamin LaHaise wrote:
> Hello everyone,
>
> Please pull the following commit (263782c1c95bbddbb022dc092fd89a36bb8d5577)
> from git://git.kvack.org/aio-fixes.git to fix an aio bug reported by Robert
> Elliot.
> ---
> As of commit f8567a3845ac05bb28f3c1b478ef752762bd39ef it is now possible to
> have put_reqs_available() called from irq context. While put_reqs_available()
> is per cpu, it did not protect itself from interrupts on the same CPU. This
> lead to aio_complete() corrupting the available io requests count when run
> under a heavy O_DIRECT workloads as reported by Robert Elliott. Fix this by
> disabling irq updates around the per cpu batch updates of reqs_available.
>
> Many thanks to Robert and folks for testing and tracking this down.
>
> Reported-by: Robert Elliot <[email protected]>
> Tested-by: Robert Elliot <[email protected]>
> Signed-off-by: Benjamin LaHaise <[email protected]>
> Cc: Jens Axboe <[email protected]>, Christoph Hellwig <[email protected]>
> Cc: [email protected]
> ---
> fs/aio.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 955947e..1c9c5f0 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -830,16 +830,20 @@ void exit_aio(struct mm_struct *mm)
> static void put_reqs_available(struct kioctx *ctx, unsigned nr)
> {
> struct kioctx_cpu *kcpu;
> + unsigned long flags;
>
> preempt_disable();
> kcpu = this_cpu_ptr(ctx->cpu);
>
> + local_irq_save(flags);
> kcpu->reqs_available += nr;
Why not just makes this:
local_irq_save(flags);
kcpu = this_put_ptr(...);
...
and get rid of the preemption bits, it's a bit redundant now you need to
kill local interrupts anyway.
--
Jens Axboe
On Mon, Jul 14, 2014 at 07:30:43PM +0200, Jens Axboe wrote:
> Why not just makes this:
>
> local_irq_save(flags);
> kcpu = this_put_ptr(...);
> ...
>
> and get rid of the preemption bits, it's a bit redundant now you need to
> kill local interrupts anyway.
*nod*. I'll add the following cleanup patch, as the first version already
got merged into another tree.
-ben
diff --git a/fs/aio.c b/fs/aio.c
index 1c9c5f0..104da62 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -832,10 +832,8 @@ static void put_reqs_available(struct kioctx *ctx, unsigned nr)
struct kioctx_cpu *kcpu;
unsigned long flags;
- preempt_disable();
- kcpu = this_cpu_ptr(ctx->cpu);
-
local_irq_save(flags);
+ kcpu = this_cpu_ptr(ctx->cpu);
kcpu->reqs_available += nr;
while (kcpu->reqs_available >= ctx->req_batch * 2) {
@@ -844,7 +842,6 @@ static void put_reqs_available(struct kioctx *ctx, unsigned nr)
}
local_irq_restore(flags);
- preempt_enable();
}
static bool get_reqs_available(struct kioctx *ctx)
@@ -853,10 +850,8 @@ static bool get_reqs_available(struct kioctx *ctx)
bool ret = false;
unsigned long flags;
- preempt_disable();
- kcpu = this_cpu_ptr(ctx->cpu);
-
local_irq_save(flags);
+ kcpu = this_cpu_ptr(ctx->cpu);
if (!kcpu->reqs_available) {
int old, avail = atomic_read(&ctx->reqs_available);
@@ -876,7 +871,6 @@ static bool get_reqs_available(struct kioctx *ctx)
kcpu->reqs_available--;
out:
local_irq_restore(flags);
- preempt_enable();
return ret;
}
-ben
--
"Thought is the essence of where you are now."