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t=1788368277; bh=egVdb9UoIL1aFUo42c4ZwNrUAMjWH0tjK9izmK9H+8E=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bRC3J1nxrhByXxV1AzoxvxllYIAt9IFtTY8uFYbNNIEThdUlLVwzKclQGJsQgyqKu wW3d/ZWibebIPxjn2Qj7i54hBJ9j3hiRHFD1tsk+2FEYBMqZH1n91FgrZ1xZ8GJDlQ p5J9cld0PMCG7FKqipexJezTLfyw3+JrG5RVTU1HvYLAnmatcb9BBFsWmR+eYiB8w+ cTRa64QUk18pJFpJCRnHG7O+1gU8Ordfg0g+cDtKi9uVV2jQROhougTPl1hpbuDRpy I1EKZrdWjGt7P1AWZ+65QJSuygNTsHiDSEHNNBNRyr9U1hWk2sS8PvA2Hqo9VATkXe ud+QOgnfWYejg== Message-ID: Date: Wed, 2 Sep 2026 18:57:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/slab: take n->list_lock in __slab_try_return_freelist() to avoid race Content-Language: en-US To: "Harry Yoo (Meta)" , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hyunwoo Kim References: <20260902-slab-fix-aba-v2-1-d1ece15a8417@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260902-slab-fix-aba-v2-1-d1ece15a8417@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 2FBC720005 X-Stat-Signature: 5j4ddxjey6d5cggubokb4tdmc8j7mino X-Rspam-User: X-HE-Tag: 1788368277-652006 X-HE-Meta: U2FsdGVkX19qK3RS4sq0zJt21XBXGzsYubxz23eE4UmeTwkRrA5vo1/RpLcpxci7qYrAeaHQ3o8DqZC+L4vo1DZnKY0wrcNoxeClEixVWEcc21K63W/qUuNDTzJJI2Ew9FjenbOBhGOzR/SJlwaTGMcUHkq/+zwwVbwMXcnRu/ht204dJ/di2fkkZHRtKBuoUDJxkn2jyvHPNzgkUaLn3ODFzaldDaXPWgWShvggWE6v3LL7/bmUgXHvR6d9Q0UE39uliii3coDspLirJRo0QTlNOI1xWuh55DZhVOsJMobxEyGrKuCe8bVyvBGYkbkA2IH4KuZEf6gZy8BWeAu3qNu3R3bmGctgiTIrwc583138OMhrBSoxT0C3KH25hLAcyQS3qfnE3t/husO0cNMDbWZRZHwsXcCM9g/REdJ2CjzO4aNRYxmBpPTHl0mu5Fzo/4umrh/0BZYKafzbq2MCoD0jCtB5YUaWYYUPX0AQAyBE1SnINmpBIb7OHrOCyfjpz+CsVYFcGlRctcoxs1V0qeyTj5CpXS1zomOOuN75IGSTbQ7As6uy1KBSnOaErEso25GFB11TPEdT2NxgyNqKPGfNj/dgjU8VLaPlkyZJILb7RP+991jEDxhJUtTBi2PwyjcDexirAsvMa4ZC4E6actNEW8u6hLzs1vXsvGlcgfMaZuiSjZjWnm9IK8BDcA28Yys9tdhTtbbx0KM1J/mKJCdIEaqW84Sgdp3u6AkbfApVMkW0n9B5zwzt4QZk6wnOh30qMxfHpMHlBS5ESy11yeL70ama8YSHCs/aZgp7v2p3GywLSbXZeSTubjGl2G8TjGdmiztihoQXNKT2N143Q8ulP+ColRfr93dusjWJHzxzgzMzlEIAl3eVSL63DevwzA/6tCLMJGhwHZOtGwW87aak5vc7QIKhqvL6nqff/GpZmIJIr25cgBTH4snoQEuUo94hkK+6Tji67qHTufb 56MlmBSa GUEgSMTLr7X4BpG5/oJiGDDz0eSQ8IgTXUeYykKzs969zsIhx0PKrNSNsSC/Zg4hVm1M2MTI4DD/YX7hJLZDwic6fjOuy+jr0gxFMHLUDFKAGyN7iq6FRHLqAGGBL3IBlerb/CIWiD8IMzDIarvyMAY4I0H7lihaMbJpenC/QXk64GBElDX30UEpbNQ3jVpACE5Hx1imDBSoNjtSEueVHsRGFl/mx2d+HUhXrObU/7LXYIpfaZg0E/DrjD9QOjrkWXeXPSfEPC54YTNlP/865Gx0SWuiorx9z80Bz0bj/3GGh98Nq5dDXGf8tE0WugnPO48RItbpkiboR/9JBVVSyEWroWMR6H9kFaLdp Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/2/26 18:41, Harry Yoo (Meta) wrote: > Commit ba7425312607 ("mm, slab: add an optimistic > __slab_try_return_freelist()") incorrectly assumed that nobody has freed > an object to the slab as long as slab->freelist is NULL and cmpxchg > succeeds. > > However, as reported by Hyunwoo Kim [1], other CPUs might have freed > an object to the slab, insert the slab to the partial list, then > allocated an object from the slab, and be in the middle of removing > the slab from the list under n->list_lock. > > Since __refill_objects_node() puts the slab back on pc.slabs > outside n->list_lock, it might insert the slab into that list while > the slab is concurrently being removed from n->partial. > This led to a list corruption, as reported by Hyunwoo Kim [1]: "as reported by ..." was already said above, we could keep just the [1] or drop completely? > list_add corruption. next->prev should be prev > (ffff888100000248), but was dead000000000122. > (next=ffffea000416e410). > kernel BUG at lib/list_debug.c:29! > Oops: invalid opcode: 0000 [#1] SMP NOPTI > CPU: 1 UID: 65534 PID: 144 Comm: poc Not tainted > 7.2.0-16172-gcf72cbb39da8-dirty #1 PREEMPT(lazy) > RIP: 0010:__list_add_valid_or_report+0x80/0xd0 > ... > Call Trace: > alloc_from_new_slab+0x183/0x300 > ___slab_alloc+0x31c/0x890 > __kmalloc_noprof+0x3d4/0x800 > lsm_blob_alloc+0x2d/0x50 > security_msg_msg_alloc+0x26/0x90 > load_msg+0x1aa/0x210 > do_msgsnd+0x91/0x800 > do_syscall_64+0x109/0x5d0 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > ... > Kernel panic - not syncing: Fatal exception > > This is a classic ABA problem where cmpxchg succeeds but the state has > changed since __refill_objects_node() took the freelist from the slab. > > As Vlastimil Babka mentioned [2], it should be rare to return more than > one slab (due to the racy read of slab->counters in > get_partial_node_bulk()). Therefore, instead of introducing additional > complexity, acquire and release n->list_lock twice in the worst case. > > Return the slab directly to the partial list and hold n->list_lock > across the cmpxchg and add_partial(). This is similar to the initial > version of commit ba7425312607 [3]. This is enough to avoid the race as > the list manipulation is serialized by n->list_lock. While at it, > bring back unlikely() hint now that the condition is unlikely. Ah nicely spotted. > Reported-by: Hyunwoo Kim > Closes: https://lore.kernel.org/linux-mm/apPa-cGLcyt90l-E@v4bel [1] > Link: https://lore.kernel.org/linux-mm/ae25c193-b95f-40c1-83b6-1c2546467e41@kernel.org [2] > Link: https://lore.kernel.org/all/20260421-b4-refill-optimistic-return-v1-1-24f0bfc1acff@kernel.org [3] > Fixes: ba7425312607 ("mm, slab: add an optimistic __slab_try_return_freelist()") > Cc: stable@vger.kernel.org > Signed-off-by: Harry Yoo (Meta) > --- > Changes in v2: > - EDITME: describe what is new in this series revision. > - EDITME: use bulletpoints and terse descriptions. > - Link to v1: https://lore.kernel.org/r/apPa-cGLcyt90l-E@v4bel > --- > mm/slub.c | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index f9b56cb439e7..5cbbacb8ee32 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5684,6 +5684,8 @@ static bool __slab_try_return_freelist(struct kmem_cache *s, struct slab *slab, > void *head, int cnt) > { > struct freelist_counters old, new; > + struct kmem_cache_node *n; > + unsigned long flags; > > old.freelist = slab->freelist; > old.counters = slab->counters; > @@ -5695,9 +5697,16 @@ static bool __slab_try_return_freelist(struct kmem_cache *s, struct slab *slab, > new.counters = old.counters; > new.inuse -= cnt; > > - if (!slab_update_freelist(s, slab, &old, &new, "__slab_try_return_freelist")) > + n = get_node(s, slab_nid(slab)); Wonder if we could just pass the 'n' to __slab_try_return_freelist() that we already have in the caller. > + spin_lock_irqsave(&n->list_lock, flags); > + > + if (!slab_update_freelist(s, slab, &old, &new, "__slab_try_return_freelist")) { > + spin_unlock_irqrestore(&n->list_lock, flags); > return false; > + } > > + add_partial(n, slab, ADD_TO_TAIL); > + spin_unlock_irqrestore(&n->list_lock, flags); > return true; > } > > @@ -7296,10 +7305,8 @@ __refill_objects_node(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int mi > void *head = object; > void *tail; > > - if (__slab_try_return_freelist(s, slab, head, count)) { > - list_add(&slab->slab_list, &pc.slabs); > + if (__slab_try_return_freelist(s, slab, head, count)) > break; > - } > > do { > tail = object; > @@ -7312,7 +7319,7 @@ __refill_objects_node(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int mi > break; > } > > - if (!list_empty(&pc.slabs)) { > + if (unlikely(!list_empty(&pc.slabs))) { > spin_lock_irqsave(&n->list_lock, flags); > > list_for_each_entry(slab, &pc.slabs, slab_list) > > --- > base-commit: cee9395acd8043be0644b25c34bfa86623f2b935 > change-id: 20260902-slab-fix-aba-d60f39fc9dee > > Best regards,