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Thu, 29 Oct 2026 07:25:02 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id epAyIs704mqrAgAAD6G6ig (envelope-from ); Thu, 29 Oct 2026 07:25:02 +0000 Message-ID: <5ed1bcc3-b586-4ec7-b8fe-beb4765fa5d8@suse.de> Date: Thu, 29 Oct 2026 08:24:54 +0100 X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 43/98] blk-mq: free the bitmaps of tags in the SRCU callback To: Jens Axboe , linux-block@vger.kernel.org Cc: Josef Bacik References: <20261028164415.1262013-1-axboe@kernel.dk> <20261028164415.1262013-44-axboe@kernel.dk> Content-Language: en-US From: Hannes Reinecke In-Reply-To: <20261028164415.1262013-44-axboe@kernel.dk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Level: X-Spamd-Result: default: False [-13.28 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-0.99)[-0.995]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; ARC_NA(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,kernel.dk:email,toxicpanda.com:email,suse.de:email] X-Spam-Score: -13.28 On 10/28/26 5:41 PM, Jens Axboe wrote: > From: Josef Bacik > > Commit ad0d05dbddc1 keeps struct blk_mq_tags and the requests until the > iterators under tags_srcu are gone, but the two bitmaps they walk are > still freed right away. When the number of hardware queues shrinks, > blk_mq_tagset_busy_iter() may be about to walk tags that > __blk_mq_update_nr_hw_queues() frees. sbitmap_free() clears the map > pointer, so that's a NULL dereference or a use-after-free, depending on > the timing. > > Free the bitmaps with the rest in the callback. > > Fixes: ad0d05dbddc1 ("blk-mq: Defer freeing of tags page_list to SRCU callback") > Signed-off-by: Josef Bacik > Signed-off-by: Jens Axboe > --- > block/blk-mq-tag.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index aaea2e2c2f23..e3edf18697af 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -623,17 +623,17 @@ static void blk_mq_free_tags_callback(struct rcu_head *head) > kmemleak_free(page_address(page)); > __free_pages(page, page->private); > } > + /* An iterator may walk the bitmaps for as long as it may see the tags */ > + sbitmap_queue_free(&tags->bitmap_tags); > + sbitmap_queue_free(&tags->breserved_tags); > kfree(tags); > } > > void blk_mq_free_tags(struct blk_mq_tags *tags) > { > - sbitmap_queue_free(&tags->bitmap_tags); > - sbitmap_queue_free(&tags->breserved_tags); > - > /* if tags pages is not allocated yet, free tags directly */ > if (list_empty(&tags->page_list)) { > - kfree(tags); > + blk_mq_free_tags_callback(&tags->rcu_head); > return; > } > Reviewed-by: Hannes Reinecke Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich