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bdev: handle unlock v. lock race

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When we unlock a range, we remove the range from the
locked bdev list before doing the for_each_channel
iteration to remove the range from each channel.

But at the same time, right after removing from the
locked list, a new lock on that range could start.
In that case, we also do a for_each_channel to add
the range to each channel, and that will race with
the for_each_channel remove.  When the lock start
wins, it finds the range already in the channel,
but doesn't set the owner_range which results in
a seg fault when the for_each_channel completes.

The fix is actually rather simple.  We just add the
locked_ctx to the comparison when checking if the
range is already in the channel.  If the locked_ctx
matches, then we know it was added as part of
initializing a new channel.  If it doesn't, then
we create a new range object pointing to the new
locked_ctx.  The first one will get removed when
the remove for_each_channel catches up.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: I94f8b20376dd437f404add35744d42fc148303ff

Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/482620
Community-CI: Broadcom SPDK FC-NVMe CI <spdk-ci.pdl@broadcom.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Paul Luse <paul.e.luse@intel.com>
Reviewed-by: Maciej Szwed <maciej.szwed@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
This commit is contained in:
Jim Harris 2020-01-23 10:22:22 -07:00 committed by Tomasz Zawadzki
parent da11a46466
commit dc3717296e
1 changed files with 6 additions and 2 deletions
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8
lib/bdev/bdev.c
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@ -2532,6 +2532,7 @@ bdev_channel_create(void *io_device, void *ctx_buf)
}
new_range->length = range->length;
new_range->offset = range->offset;
new_range->locked_ctx = range->locked_ctx;
TAILQ_INSERT_TAIL(&ch->locked_ranges, new_range, tailq);
}
@ -6110,7 +6111,9 @@ bdev_lock_lba_range_get_channel(struct spdk_io_channel_iter *i)
struct lba_range *range;
TAILQ_FOREACH(range, &ch->locked_ranges, tailq) {
if (range->length == ctx->range.length && range->offset == ctx->range.offset) {
if (range->length == ctx->range.length &&
range->offset == ctx->range.offset &&
range->locked_ctx == ctx->range.locked_ctx) {
/* This range already exists on this channel, so don't add
* it again. This can happen when a new channel is created
* while the for_each_channel operation is in progress.
@ -6260,7 +6263,8 @@ bdev_unlock_lba_range_get_channel(struct spdk_io_channel_iter *i)
TAILQ_FOREACH(range, &ch->locked_ranges, tailq) {
if (ctx->range.offset == range->offset &&
ctx->range.length == range->length) {
ctx->range.length == range->length &&
ctx->range.locked_ctx == range->locked_ctx) {
TAILQ_REMOVE(&ch->locked_ranges, range, tailq);
free(range);
break;