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Subject[PATCH] aio: Wake all waiters when destroying ctx
Date
From: Roland Dreier <roland@purestorage.com>

The test program below will hang because io_getevents() uses
add_wait_queue_exclusive(), which means the wake_up() in io_destroy()
only wakes up one of the threads. Fix this by using wake_up_all() in
the aio code paths where we want to make sure no one gets stuck.

// t.c -- compile with gcc -lpthread -laio t.c

#include <libaio.h>
#include <pthread.h>
#include <stdio.h>
#include <unistd.h>

static const int nthr = 2;

void *getev(void *ctx)
{
struct io_event ev;
io_getevents(ctx, 1, 1, &ev, NULL);
printf("io_getevents returned\n");
return NULL;
}

int main(int argc, char *argv[])
{
io_context_t ctx = 0;
pthread_t thread[nthr];
int i;

io_setup(1024, &ctx);

for (i = 0; i < nthr; ++i)
pthread_create(&thread[i], NULL, getev, ctx);

sleep(1);

io_destroy(ctx);

for (i = 0; i < nthr; ++i)
pthread_join(thread[i], NULL);

return 0;
}

Cc: <stable@kernel.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>
---
fs/aio.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 26869cd..88f0ed5 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -520,7 +520,7 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
ctx->reqs_active--;

if (unlikely(!ctx->reqs_active && ctx->dead))
- wake_up(&ctx->wait);
+ wake_up_all(&ctx->wait);
}

static void aio_fput_routine(struct work_struct *data)
@@ -1229,7 +1229,7 @@ static void io_destroy(struct kioctx *ioctx)
* by other CPUs at this point. Right now, we rely on the
* locking done by the above calls to ensure this consistency.
*/
- wake_up(&ioctx->wait);
+ wake_up_all(&ioctx->wait);
put_ioctx(ioctx); /* once for the lookup */
}


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