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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1765799902; bh=p3ib7IxATEEQKs6tLDHHrhEZu0aHnPihiAgww66H4cQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KcjMJ031jvj8WbTNzax5HHRcg5ddvgbwkfIjEdJiKCj5AO9fB/6pDavbpha3Eh9Re 69g2/ys0cw/30gkkLda5wgsOEG0YlOvhlHVi8pbg2F6TQyey50Qj86YAgbPZjEeL0y FiXvIzdA2XRU97NAahkk5YQVyUKU64nPnkKPPQu/2W/XpbtyIfvZ+ULo0SM8G6gtns QQcOf+Amu5/D4vFoimmq/PWFQWsUM7fDRmb5KZvC0T7jgDgmdm8LUBaR/HDLFHnha/ tNgqhvaMkdBSy9Z8hw8yRCxIAufG77TMkjr9cGgiL13g4iNVvUqqo4jcxCNaJPdchj vFor6C4D0hRJA== Date: Mon, 15 Dec 2025 12:58:17 +0100 From: Christian Brauner To: Al Viro Cc: Hugh Dickins , Miklos Szeredi , Andrew Morton , Baolin Wang , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Chuck Lever Subject: Re: [RFC][PATCH 2/2] shmem: fix recovery on rename failures Message-ID: <20251215-mythologisch-losung-f99a7be1c735@brauner> References: <47e9d03c-7a50-2c7d-247d-36f95a5329ed@google.com> <20251212050225.GD1712166@ZenIV> <20251212053452.GE1712166@ZenIV> <8ab63110-38b2-2188-91c5-909addfc9b23@google.com> <20251212063026.GF1712166@ZenIV> <2a102c6d-82d9-2751-cd31-c836b5c739b7@google.com> <20251213072241.GH1712166@ZenIV> <20251214032734.GL1712166@ZenIV> <20251214033049.GB460900@ZenIV> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20251214033049.GB460900@ZenIV> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 6B6F6A000C X-Stat-Signature: m6mm1rt9goizeii44h77rd5tek7qt8ti X-Rspam-User: X-HE-Tag: 1765799903-185209 X-HE-Meta: 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 7upst39F L9xWTcDGCpFg09ylynkn4qwkLRvWgFbw/XFYzv0LITEW90/MToA0zQJ78LmZ4Zf7MmuY8rhlxfRfZUo7Jpgj6prZfoUJyRrYtoYyl91yXNLMrrHT8J4JwBKLSo0JNxbYuX/modGNKjVYxhNPKYqIxejg24R9waHyQM5ysMggv8pQ1cZ2HnwooeIhLxd7ZStA3RxI4CeR9TijMO3Q+Sv3qrdhLNDOE6GF+35p0ffqRc1kFJP7ot6iIUdncT2c2dDI++MZEsi3edDxUna8XASKp7+YybGv/i5uyTOghyZd6MeHiqQcaxcn4pqv4FVcAAkX3wM0TAUK2fh3dmfwg2QlCo982t3lNpgDXlGafME2jTfs1gPU4Iascr0FBMedR46t28BQi X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Dec 14, 2025 at 03:30:49AM +0000, Al Viro wrote: > maple_tree insertions can fail if we are seriously short on memory; > simple_offset_rename() does not recover well if it runs into that. > The same goes for simple_offset_rename_exchange(). > > Moreover, shmem_whiteout() expects that if it succeeds, the caller will > progress to d_move(), i.e. that shmem_rename2() won't fail past the > successful call of shmem_whiteout(). > > Not hard to fix, fortunately - mtree_store() can't fail if the index we > are trying to store into is already present in the tree as a singleton. > > For simple_offset_rename_exchange() that's enough - we just need to be > careful about the order of operations. > > For simple_offset_rename() solution is to preinsert the target into the > tree for new_dir; the rest can be done without any potentially failing > operations. > > That preinsertion has to be done in shmem_rename2() rather than in > simple_offset_rename() itself - otherwise we'd need to deal with the > possibility of failure after successful shmem_whiteout(). > > Fixes: a2e459555c5f ("shmem: stable directory offsets") > Signed-off-by: Al Viro > --- Looks good to me, Reviewed-by: Christian Brauner